Image heating apparatus and image forming apparatus

ABSTRACT

An image heating apparatus includes a heater having a plurality of heat generating elements, a roller for forming a nip portion with the heater, an acquisition portion that acquires a plurality of count values indicating heat accumulation amounts of a plurality of heating regions heated by the plurality of heat generating elements, respectively, and a control portion that controls electrical power to be supplied to the plurality of heat generating elements to control individual heat generating quantities of the plurality of heat generating elements. The control portion controls the heat generating quantities so that a difference between a first count value indicating a heat accumulation amount of a first heating region heated by a first heat generating element and a second count value indicating a heat accumulation amount of a second heating region heated by a second heat generating element is maintained within a predetermined range.

This application is a continuation application of U.S. patentapplication Ser. No. 15/876,455, filed Jan. 22, 2018, which claims thebenefit of Japanese Patent Application No. 2017-012046, filed on Jan.26, 2017, all of which are hereby incorporated by reference herein intheir entireties.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to an image forming apparatus, such as acopying machine or a printer, which uses an electrophotographic systemor an electrostatic recording system. Moreover, the present inventionrelates to an image heating apparatus, such as a fixing unit mounted inan image forming apparatus, or a gloss applying apparatus that improvesa gloss level of a toner image by re-heating the toner image fixed to arecording material.

Description of the Related Art

In an image heating apparatus, such as a fixing unit or a gloss applyingapparatus, used in an electrophotographic image forming apparatus(hereafter an image forming apparatus), such as a copying machine or aprinter, a method of selectively heating image portions formed on arecording material has been proposed in order to save power (seeJapanese Patent Application Publication No. H06-95540). In this method,a heat generation range of a heater is divided into a plurality of heatgenerating blocks in a longitudinal direction (a direction orthogonal toa conveying direction of the recording material), and heat generation ofrespective heat generating blocks is selectively controlled depending onthe presence of an image on the recording material. That is,energization of a heat generating block in a portion in which an imageis not formed (a non-image portion) on the recording material is stoppedto save power.

On the other hand, there is a demand to increase a recording materialprocessing speed per unit time of the image heating apparatus to enhanceimage productivity. Therefore, it is requested to increase a recordingmaterial conveying speed. When a recording material conveying speed insuch an image heating apparatus of Embodiment 11, as disclosed inJapanese Patent Application Publication No. H06-95540, increases, whenenergization control is switched from a non-image portion (anenergization stop state) to an image portion, since a heating time isshort, there may be a case in which the image portion cannot besufficiently heated to a control temperature. In order to prevent thisproblem, a method of performing energization control so that thetemperature reaches a predetermined control temperature at the time ofswitching to energization of a heat generating block of the non-imageportion to thereby allow the temperature to quickly reach the controltemperature of the image portion has been considered. In this case, thecontrol temperature of the image portion is set to be less than thecontrol temperature of the non-image portion so that both a power savingeffect and image productivity can be achieved.

In an image heating apparatus that performs heat generation controlusing different control temperatures for respective heat generatingblocks, however, a variation may occur in a heat accumulation state ofrespective heat generating blocks. As a result, this variation may causea recording material conveying defect, such as a paper wrinkle or atrailing edge pop-up, thereby increasing a load applied to a fixingmember, and decreasing a durability of constituent members. That is, inan image heating apparatus having heat generating blocks divided in thelongitudinal direction, since the heat generating quantities ofrespective heat generating blocks differ depending on an image patternon a recording material that passes through the heat generating block, aheat accumulation state of the fixing member is different in respectiveheat generating blocks. Since a roller, or the like, used in the fixingmember is thermally expanded according to the heat accumulation amount,a recording material conveying performance or a rotational driving forceof the fixing member is different in respective heat generating blocks.Therefore, due to a difference in conveying performance or rotationaldriving force of heat generating blocks in the image heating apparatus,there is a possibility that a conveying defect, such as a paper wrinkleor a trailing edge pop-up, may occur in a recording material. Moreover,since the rotational driving force of the fixing member is different inthe longitudinal direction of the image heating apparatus, there is apossibility that the force of pulling a fixing film in one directionincreases and the durability of the fixing film or a pressure rollerdecreases.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a technology capable ofenhancing a power saving function while suppressing the occurrence of arecording material conveying defect and a decrease in durability of afixing member.

In order to achieve the object described above, one aspect of theinvention provides an image heating apparatus including a heater havinga plurality of heat generating elements arranged in a longitudinaldirection orthogonal to a conveying direction of a recording material,and a control portion capable of controlling electrical power to besupplied to the plurality of heat generating elements to controlindividual heat generating quantities of the plurality of heatgenerating elements, wherein an image formed on the recording materialis heated by the heat generated by the heater, wherein the image heatingapparatus comprises an acquisition portion that acquires a plurality ofcount values indicating heat accumulation amounts of a plurality ofheating regions heated by the plurality of heat generating elements, andwherein the control portion controls the heat generating quantities ofthe plurality of heat generating elements so that a difference between afirst count value indicating a heat accumulation amount of a heatingregion heated by a first heat generating element among the plurality ofheat generating elements and a second count value indicating a heataccumulation amount of a heating region heated by a second heatgenerating element among the plurality of heat generating elements ismaintained within a predetermined range.

In order to achieve the object described above, another aspect of theinvention provides an image forming apparatus including an image formingportion that forms an image on a recording material, and a fixingportion that fixes the image formed on the recording material, to therecording material, wherein the fixing portion is the image heatingapparatus.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments, with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an image forming apparatus accordingto an embodiment of the present invention.

FIG. 2 is a cross-sectional view of an image heating apparatus accordingto Embodiment 1.

FIGS. 3A to 3C are diagrams illustrating a configuration of a heateraccording to Embodiment 1.

FIG. 4 is a diagram of a heater control circuit according to Embodiment1.

FIG. 5 is a diagram illustrating a heating region according toEmbodiment 1.

FIG. 6 is a flowchart for determining a classification and a controltemperature of a heating region according to Embodiment 1.

FIGS. 7A to 7C illustrate a specific example of the classification ofthe heating region according to Embodiment 1.

FIGS. 8A to 8C illustrate setting values of parameters associated withthe control temperature according to Embodiment 1.

FIGS. 9A to 9D illustrate setting values of parameters associated with aheat accumulation count value according to Embodiment 1.

FIGS. 10A to 10C are diagrams for describing specific exemplaryrecording materials according to Embodiment 1.

FIG. 11 is a flowchart for determining a classification and a controltemperature of a heating region according to a comparative example.

FIGS. 12A to 12C are diagrams for describing an advantage of Embodiment1.

FIG. 13A is a flowchart for determining a classification and a controltemperature of a heating region according to Embodiment 2.

FIGS. 13B and 13C illustrate setting values of parameters associatedwith the control temperature according to Embodiment 2.

FIGS. 14A to 14C are diagrams for describing an advantage of Embodiment2.

FIG. 15A is a flowchart for determining a classification and a controltemperature of a heating region according to Embodiment 3.

FIGS. 15B and 15C illustrate setting values of parameters associatedwith the control temperature according to Embodiment 3.

FIGS. 16A and 16B are diagrams for describing specific exemplaryrecording materials according to Embodiment 3.

FIGS. 17A to 17C are diagrams for describing an advantage of Embodiment3.

FIG. 18 is a flowchart for determining a classification and a controltemperature of a heating region according to Embodiment 4.

FIGS. 19A and 19B are diagrams for describing a specific example ofEmbodiment 4.

FIGS. 20A to 20C are diagrams for describing an advantage of Embodiment4.

DESCRIPTION OF THE EMBODIMENTS

Hereafter, a description will be given, with reference to the drawings,of embodiments (examples) of the present invention. The sizes,materials, shapes, their relative arrangements, or the like, ofconstituents described in the embodiments may, however, be appropriatelychanged according to the configurations, various conditions, or thelike, of apparatuses to which the invention is applied. Therefore, thesizes, the materials, the shapes, their relative arrangements, or thelike, of the constituents described in the embodiments do not limit thescope of the invention to the following embodiments.

Embodiment 1 1. Configuration of Image Forming Apparatus

FIG. 1 is a schematic cross-sectional view of an image forming apparatusaccording to an embodiment of the present invention. Examples of animage forming apparatus to which the present invention can be appliedinclude a copying machine, a printer, and the like, that use anelectrophotographic scheme or an electrostatic recording scheme. In thisembodiment, a case in which the present invention is applied to a laserprinter will be discussed.

When a print signal is generated, a scanner unit 21 emits a laser beammodulated according to image information to scan a photosensitive drum19 that is charged to a predetermined polarity by a charging roller 16.In this way, an electrostatic latent image is formed on thephotosensitive drum 19. When toner is supplied from a developing roller17 to the electrostatic latent image, the electrostatic latent image onthe photosensitive drum 19 is developed as a toner image. Meanwhile, arecording material (a recording sheet) P stacked on a sheet feedcassette 11 is fed by a pickup roller 12 one by one, and is conveyedtoward a registration roller pair 14 by a conveying roller pair 13.Furthermore, the recording material P is conveyed from the registrationroller pair 14 to a transfer position in synchronization with a timingat which the toner image on the photosensitive drum 19 reaches atransfer position formed by the photosensitive drum 19 and a transferroller 20. The toner image on the photosensitive drum 19 is transferredto the recording material P in the course in which the recordingmaterial P passes through the transfer position. After that, therecording material P is heated by a fixing apparatus 200 as a fixingportion of an image heating apparatus, and the toner image is heated andfixed to the recording material P. The recording material P that bearsthe toner image fixed thereto is discharged to a tray in an upper partof the image forming apparatus 100 by conveying roller pairs 26 and 27.

Reference numeral 18 is a drum cleaner that cleans the photosensitivedrum 19, and reference numeral 28 is a sheet feed tray (a manual tray)having a pair of recording material regulating plates, the width ofwhich can be adjusted according to the size of the recording material P.The sheet feed tray 28 is provided so as to support a recording materialP having a size other than standard sizes. Reference numeral 29 is apickup roller that feeds the recording material P from the sheet feedtray 28, and reference numeral 30 is a motor that drives the fixingapparatus 200, and the like. A control circuit 400, as heater drivingmeans connected to a commercial alternating-current power supply 401,supplies electrical power to the fixing apparatus 200. Thephotosensitive drum 19, the charging roller 16, the scanner unit 21, thedeveloping roller 17, and the transfer roller 20 form an image formingportion that forms a non-fixed image on the recording material P. In thepresent embodiment, the photosensitive drum 19, the charging roller 16,a developing unit including the developing roller 17, and a cleaningunit including the drum cleaner 18 are configured as a process cartridge15 so as to be detachably attached to a main body of the image formingapparatus 100.

The image forming apparatus 100 of the present embodiment is configuredsuch that a largest sheet passing width in a direction orthogonal to theconveying direction of the recording material P is 216 mm, and the imageforming apparatus 100 can print 44.3 pages of a standard sheet of aletter (LTR) size (216 mm×279 mm) per minute at a conveying speed of232.5 mm/sec.

2. Configuration of Image Heating Apparatus

FIG. 2 is a schematic cross-sectional view of the fixing apparatus 200as the image heating apparatus of the present embodiment. The fixingapparatus 200 includes a fixing film 202 as an endless belt, a heater300 that makes contact with an inner surface of the fixing film 202, apressure roller 208 that forms a fixing nip portion N together with theheater 300 with the fixing film 202 interposed therebetween, and a metalstay 204.

The fixing film 202 is a heat-resistant multilayer film formed in atubular form, and a heat-resistant resin, such as polyimide, or a metal,such as stainless steel, is used as a base layer of the fixing film 202.Moreover, the surface of the fixing film 202 is coated with aheat-resistant resin with excellent releasability, such as atetrafluoroethylene-perfluoro (alkyl vinyl ether) copolymer (PFA), inorder to prevent toner adhesion and to secure separability from therecording material P to thereby form a releasing layer thereon.Furthermore, in an image forming apparatus 100 that forms color imagesparticularly, in order to improve image quality, a heat-resistantrubber, such as silicone rubber, may be formed between the base layerand the releasing layer as an elastic layer. The pressure roller 208includes a metal core 209 formed of a material, such as iron oraluminum, and an elastic layer 210 formed of a material, such as siliconrubber. The heater 300 is held by a heater holding member 201 formed ofa heat-resistant resin, and heats heating regions A₁ to A₇ (the detailswill be described later) provided in the fixing nip portion N to therebyheat the fixing film 202. The heater holding member 201 also has aguiding function of guiding rotation of the fixing film 202. Anelectrode E is provided in the heater 300 on an opposite side of thefixing nip portion N, and electrical power is fed from an electricalcontact C to the electrode E. The metal stay 204 receives a pressurizingforce (not illustrated) and biases the heater holding member 201 towardthe pressure roller 208. Moreover, a safety element 212 that is athermo-switch, a temperature fuse, or the like, and that is actuated inthe event of abnormal heat generation of the heater 300 to interruptelectrical power supplied to the heater 300, is in direct contact withthe heater 300 or in indirect contact with the heater 300 with theheater holding member 201 interposed therebetween.

The pressure roller 208 rotates in a direction indicated by arrow R1 inresponse to motive power from the motor 30. The fixing film 202 rotatesin a direction indicated by arrow R2 following the rotation of thepressure roller 208. The heat of the fixing film 202 is applied to therecording material P while being conveyed in a state of being pinched atthe fixing nip portion N whereby the non-fixed toner image on therecording material P is fixed. Moreover, in order to secure slidabilityof the fixing film 202 and to obtain a stable rotation state, alubricant (not illustrated) having high heat resistance is interposedbetween the heater 300 and the fixing film 202.

3. Configuration of Heater

A configuration of the heater 300 according to the present embodimentwill be described with reference to FIGS. 3A to 3C. FIG. 3A is across-sectional view of the heater 300, FIG. 3B is a plan view ofrespective layers of the heater 300, and FIG. 3C is a diagram fordescribing a method of connecting the electrical contact C to the heater300. FIG. 3B illustrates a conveying reference position X of therecording material P in the image forming apparatus 100 of the presentembodiment. The conveying reference position X in the present embodimentis set to a center of the recording material P, and the recordingmaterial P is conveyed so that a central line in a direction orthogonalto the conveying direction follows the conveying reference position X.Moreover, FIG. 3A is a cross-sectional view of the heater 300 at theconveying reference position X.

The heater 300 includes a ceramic substrate 305, a back surface layer 1provided on the substrate 305, a back surface layer 2 that covers theback surface layer 1, a sliding surface layer 1 provided on a surface onthe opposite side of the back surface layer 1 on the substrate 305, anda sliding surface layer 2 that covers the sliding surface layer 1.

The back surface layer 1 has conductors 301 (301 a and 301 b) providedalong the longitudinal direction of the heater 300. The conductor 301 isdivided into the conductors 301 a and 301 b, and the conductor 301 b isdisposed on a downstream side in the conveying direction of therecording material P in relation to the conductor 301 a. Moreover, theback surface layer 1 has conductors 303 (303-1 to 303-7) provided inparallel to the conductors 301 a and 301 b. The conductors 303 areprovided between the conductors 301 a and 301 b along the longitudinaldirection of the heater 300.

Furthermore, the back surface layer 1 has a heat generating element 302a (302 a-1 to 302 a-7) and a heat generating element 302 b (302 b-1 to302 b-7) that are heat generating resistors that generate heat uponenergization. The heat generating elements 302 a are provided betweenthe conductors 301 a and 303 so as to generate heat in response toelectrical power supplied via the conductors 301 a and 303. The heatgenerating elements 302 b are provided between the conductors 301 b and303 so as to generate heat in response to electrical power supplied viathe conductors 301 b and 303.

A heat generating portion that includes the conductor 301, the conductor303, the heat generating element 302 a, and the heat generating element302 b is divided into seven heat generating blocks (HB₁ to HB₇) withrespect to the longitudinal direction of the heater 300. That is, theheat generating element 302 a is divided into seven regions of heatgenerating elements 302 a-1 to 302 a-7 with respect to the longitudinaldirection of the heater 300. Moreover, the heat generating element 302 bis divided into seven regions of heat generating elements 302 b-1 to 302b-7 with respect to the longitudinal direction of the heater 300.Furthermore, the conductor 303 is divided into seven regions ofconductors 303-1 to 303-7 in alignment with the dividing positions ofthe heat generating elements 302 a and 302 b. The seven heat generatingblocks (HB₁ to HB₇) are configured such that the amounts of energizationof heat generating resistors in the respective blocks are controlledindividually, whereby the heat generating quantities of the respectiveheat generating blocks are controlled individually.

In the present embodiment, a heat generating range ranges from the leftend in FIG. 3B of the heat generating block HB₁ to the right end in FIG.3B of the heat generating block HB₇, and the entire length is 220 mm.Moreover, the longitudinal lengths of respective heat generating blocksare approximately the same as 31 mm, but the lengths may be differentfrom each other.

Moreover, the back surface layer 1 has electrodes E (E1 to E7, E8-1, andE8-2). The electrodes E1 to E7 are provided within the regions of theconductors 303-1 to 303-7, respectively, and are electrodes forsupplying electrical power to the heat generating blocks HB₁ to HB₇ viathe conductors 303-1 to 303-7, respectively. The electrodes E8-1 andE8-2 are provided at the ends in the longitudinal direction of theheater 300 so as to be connected to the conductor 301, and areelectrodes for supplying electrical power to the heat generating blocksHB₁ to HB₇ via the conductor 301. In the present embodiment, althoughthe electrodes E8-1 and E8-2 are provided at both ends in thelongitudinal direction of the heater 300, the electrode E8-1 only may beprovided on one end, for example. Moreover, although electrical power issupplied to the conductors 301 a and 301 b using a common electrode,individual electrodes may be provided to the conductors 301 a and 301 b,and electrical power may be supplied via the respective electrodes.

The back surface layer 2 is configured as a surface protection layer 307having an insulating property (in the present embodiment, formed ofglass) and covers the conductor 301, the conductor 303, and the heatgenerating elements 302 a and 302 b. Moreover, the surface protectionlayer 307 is formed in a region outside the portions of the electrodes Eso that the electrical contacts C can be connected to the electrodes Efrom the side of the back surface layer 2 of the heater 300.

The sliding surface layer 1 is provided on a surface of the substrate305 on the opposite side of a surface on which the back surface layer 1is provided, and has thermistors TH (TH1-1 to TH1-4 and TH2-5 to TH2-7)as detection means for detecting the temperature of the heat generatingblocks HB₁ to HB₇. Each thermistor TH is formed of a material having PTCcharacteristics or NTC characteristics (in the present embodiment, NTCcharacteristics), and can detect the temperature of all heat generatingblocks HB₁ to HB₇ by detecting the resistance thereof.

Moreover, the sliding surface layer 1 has conductors ET (ET1-1 to ET1-4and ET2-5 to ET2-7) and conductors EG (EG1 and EG2) in order to energizethe thermistor TH to detect the resistance thereof. The conductors ET1-1to ET1-4 are connected to the thermistors TH1-1 to TH1-4, respectively.The conductors ET2-5 to ET2-7 are connected to the thermistors TH2-5 toTH2-7, respectively. The conductor EG1 is connected to four thermistorsTH1-1 to TH1-4 to form a common conduction path. The conductor EG2 isconnected to three thermistors TH2-5 to TH2-7 to form a commonconduction path. The conductors ET and EG are formed up to thelongitudinal ends along the longitudinal direction of the heater 300,and are connected to the control circuit 400 via electrical contacts(not illustrated) at the longitudinal ends of the heater 300.

The sliding surface layer 2 is formed of a surface protection layer 308having slidability and an insulating property (in the presentembodiment, formed of glass), and is configured to cover the thermistorTH and the conductors ET and EG, and to secure the ability to slide onthe inner surface of the fixing film 202. Moreover, the surfaceprotection layer 308 is formed in a region outside both ends in thelongitudinal direction of the heater 300 in order to provide electricalcontacts for the conductors ET and EG.

Subsequently, a method of connecting the electrical contacts C to therespective electrodes E will be described. FIG. 3C is a plan viewillustrating a state in which the electrical contacts C are connected tothe respective electrodes E as seen from the heater holding member 201.Through-holes are formed in the heater holding member 201 at positionscorresponding to the electrodes E (E1 to E7, E8-1, and E8-2). At thepositions of the respective through-holes, the electrical contacts C (C1to C7, C8-1, and C8-2) are electrically connected to the electrodes E(E1 to E7, E8-1, and E8-2) by a method such as spring-based biasing orwelding. The electrical contacts C are connected to the control circuit400 (to be described later) of the heater 300 by a conductive material(not illustrated) provided between the metal stay 204 and the heaterholding member 201.

4. Configuration of Heater Control Circuit

FIG. 4 illustrates a computer program of the control circuit 400 of theheater 300 according to Embodiment 1. Reference numeral 401 is acommercial alternating-current power supply connected to the imageforming apparatus 100. The electrical power supplied to the heater 300is controlled by energization/de-energization of triacs 411 to 417. Thetriacs 411 to 417 operate according to signals FUSER1 to FUSER7,respectively, from a CPU 420. The driving circuit of the triacs 411 to417 is not illustrated. The control circuit 400 of the heater 300 isconfigured to be able to individually control the seven heat generatingblocks HB₁ to HB₇ using the seven triacs 411 to 417, respectively. Azero cross detector 421 is a circuit that detects zero cross of thealternating-current power supply 401 and outputs a signal ZEROX to theCPU 420. The signal ZEROX is used for detecting the timings of phase orfrequency control of the triacs 411 to 417.

A method of detecting the temperature of the heater 300 will bedescribed. The temperature of the heater 300 is detected by thethermistors TH (TH1-1 to TH1-4 and TH2-5 to TH2-7). Voltages divided bythe thermistors TH1-1 to TH1-4 and resistors 451 to 454 are detected bythe CPU 420 as signals Th1-1 to Th1-4, and the CPU 420 converts thesignals Th1-1 to Th1-4 to temperatures. Similarly, voltages divided bythermistors TH2-5 to TH2-7 and resistors 465 to 467 are detected by theCPU 420 as signals Th2-5 to Th2-7, and the CPU 420 converts the signalsTh2-5 to Th2-7 to temperatures.

Internal processing of the CPU 420 involves calculating electrical powerto be supplied by PI control (proportional integral control), forexample, on the basis of control temperatures (control targettemperatures) TGT_(i) of respective heat generating blocks to bedescribed later, and the detection temperatures of the thermistors TH.Furthermore, the CPU 420 converts the electrical power to be supplied toa control level of a phase angle (phase control) or a frequency(frequency control) corresponding to the electrical power, and controlsthe triacs 411 to 417 according to the control condition. The CPU 420executes energization control and various operations associated withtemperature control of the heater 300 as a control portion and anacquisition portion of the present invention.

Relays 430 and 440 are used as means for interrupting the supply ofelectrical power to the heater 300 when the temperature of the heater300 increases excessively due to a fault, or the like. A circuitoperation of the relays 430 and 440 will be described. When a signalRLON changes to the High state, a transistor 433 enters into the ONstate, a current flows from a supply voltage node Vcc to asecondary-side coil of the relay 430, and a primary-side contact of therelay 430 enters into the ON state. When the signal RLON changes to theLow state, the transistor 433 enters into the OFF state, the currentflowing from the supply voltage node Vcc to the secondary-side coil ofthe relay 430 is interrupted, and the primary-side contact of the relay430 enters into the OFF state. Similarly, when the signal RLON changesto the High state, a transistor 443 enters into the ON state, a currentflows from a supply voltage node Vcc to a secondary-side coil of therelay 440, and a primary-side contact of the relay 440 enters into theON state. When the signal RLON changes to the Low state, the transistor443 enters into the OFF state, the current flowing from the supplyvoltage node Vcc to the secondary-side coil of the relay 440 isinterrupted, and the primary-side contact of the relay 440 enters intothe OFF state. Resistors 434 and 444 are current limiting resistors.

Next, the operation of a safety circuit that uses the relays 430 and 440will be described. When any one of the temperatures detected by thethermistors TH1-1 to TH1-4 exceeds a predetermined value set thereto, acomparator 431 operates a latch 432, and the latch 432 latches a signalRLOFF1 to the Low state. When the signal RLOFF1 changes to the Lowstate, the relay 430 can be maintained in the OFF state (a stable state)since the transistor 433 is maintained in the OFF state even when theCPU 420 puts the signal RLON into the High state. In a non-latchedstate, the signal RLOFF1 of the latch 432 enters into the open state.When any one of the temperatures detected by the thermistors TH2-5 toTH2-7 exceeds a predetermined value set thereto, a comparator 441operates a latch 442, and the latch 442 latches a signal RLOFF2 to theLow state. When the signal RLOFF2 changes to the Low state, the relay440 can be maintained in the OFF state (a stable state) since thetransistor 443 is maintained in the OFF state even when the CPU 420 putsthe signal RLON into the High state. Similarly, in a non-latched state,the signal RLOFF2 of the latch 442 enters into the open state.

5. Heating Region

FIG. 5 is a diagram illustrating heating regions A₁ to A₇, according tothe present embodiment, that are illustrated in comparison with a sheetwidth of a LETTER (LTR)-size sheet. The heating regions A₁ to A₇ areprovided at positions corresponding to the heat generating blocks HB₁ toHB₇ in the fixing nip portion N, and the heating regions A_(i) (i=1 to7) are heated when the heat generating blocks HB_(i) (i=1 to 7) generateheat. The entire length of the heating regions A₁ to A₇ is 220 mm, andthe respective regions are obtained by evenly dividing the entire lengthinto seven parts (L=31.4 mm).

A specific example of a classification of the heating region A_(i) willbe described with reference to FIGS. 7A to 7C. In the presentembodiment, the recording material P passing through the fixing nipportion N is segmented in the conveying direction every predeterminedperiod, and the heating regions A_(i) are classified in respectivesegments. In the present embodiment, the recording material P issegmented every 0.24 seconds on the basis of a leading edge thereof as areference, so that the recording material P is segmented into fivesegments, such that the first segment is the segment T₁, the secondsegment is the segment T₂, the third segment is the segment T₃, thefourth segment is the segment T₄, and the fifth segment is the segmentT₅. In a specific example, the recording material P is the LTR-sizesheet and passes through the heating regions A₁ to A₇ in that order.When the recording material and an image are present at the positionillustrated in FIG. 7A, the heating regions A_(i) are classified asillustrated in the tables of FIGS. 7B and 7C.

Each of the heating regions A_(i) (i=1 to 7) is classified into arecording material edge region AE, a recording material central regionAM, an image heating region AI, and a non-image heating region AP. Whena recording material edge PE passes through the heating region A_(i),the heating region A_(i) is classified as the recording material edgeregion AE. When a recording material central portion other than therecording material edge PE passes through the heating region A_(i), theheating region A_(i) is classified as the recording material centralregion AM. The recording material edge PE determined herein is anextreme edge PE in the direction orthogonal to the conveying directionof the recording material P as illustrated in FIG. 7A. When an imagerange passes through the heating region A_(i), the heating region A_(i)is classified as the image heating region AI. When a region other thanthe image range passes through the heating region A_(i), the heatingregion A_(i) is classified as the non-image heating region AP. Theclassification of the heating region A_(i) is used for controlling theheat generating quantity of the heat generating block HB_(i), as will bedescribed later.

That is, by the classification based on the recording material sizeinformation, the heating regions A₁ and A₇ are classified as therecording material edge region AE and the recording material edge PEpasses through the heating regions A₁ and A₇. Moreover, the heatingregions A₂, A₃, A₄, A₅, and A₆ are classified as the recording materialcentral region AM. A heat generating element that forms the heatingregions A₁ and A₇ corresponds to a first heat generating element of thepresent invention, and a heat generating element that forms the heatingregions A₂, A₃, A₄, A₅, and A₆ corresponds to a second heat generatingelement of the present invention. Moreover, according to image data(image information), in the segment T₁, the heating regions A₁, A₂, A₃,and A₄ are classified as the image heating region AI since the imagerange passes through the heating regions A₁, A₂, A₃, and A₄, and theheating regions A₅, A₆, A₇ are classified as the non-image heatingregion AP since the image range does not pass through the heatingregions A₅, A₆, and A₇. In the segments T₂ to T₅, the heating regionsA₂, A₃, A₄, A₅, and A₆ are classified as the image heating region AIsince the image range passes through the heating regions A₂, A₃, A₄, A₅,and A₆, and the heating regions A₁ and A₇ are classified as thenon-image heating region AP since the image range does not pass throughthe heating regions A₁ and A₇.

6. Overview of Heater Control Method

Next, a heater control method according to the present embodiment (thatis, a method of controlling the heat generating quantity of the heatgenerating block HB_(i) (i=1 to 7)) will be described. The heatgenerating quantity of the heat generating block HB_(i) is determined bythe electrical power supplied to the heat generating block HB_(i). Theheat generating quantity of the heat generating block HB_(i) increaseswhen the electrical power supplied to the heat generating block HB_(i)is increased, and the heat generating quantity of the heat generatingblock HB_(i) decreases when the electrical power supplied to the heatgenerating block HB_(i) is decreased. The electrical power supplied tothe heat generating block HB_(i) is calculated on the basis of thecontrol temperatures TGT_(i) (i=1 to 7) set to respective heatgenerating blocks and the temperature detected by the thermistor. In thepresent embodiment, the supplied electrical power is calculated by PIcontrol (proportional integral control), so that the temperaturesdetected by the respective thermistors are equal to the controltemperatures TGT_(i) of the respective heat generating blocks HB_(i).The control temperatures TGT_(i) of the respective heat generatingblocks HB_(i) are set according to the classification of the heatingregions A_(i) determined by the flow of FIG. 6.

FIG. 6 is a flowchart for determining a classification and a controltemperature of the heating region according to the present embodiment.As illustrated in the flowchart of FIG. 6, the respective heatingregions A_(i) (i=1 to 7) are classified into the recording material edgeregion AE, the recording material central region AM, the image heatingregion AI, the non-image heating region AP, and a recording materialedge heating correction region AW. The heating region A_(i) isclassified on the basis of image data (image information) and recordingmaterial information (a recording material size) sent from an externalapparatus (not illustrated), such as a host computer.

That is, on the basis of the size information of a recording material P,it is determined whether the heating region A_(i) is a region throughwhich the recording material edge PE passes, or a region through which aregion other than the recording material edge PE passes (S1002). Whenthe recording material edge PE passes through the heating region A_(i),the heating region A_(i) is classified as the recording material edgeregion AE (S1003). When the recording material central portion otherthan the recording material edge PE passes through the heating regionA_(i), the heating region A_(i) is classified as the recording materialcentral region AM (S1004). Subsequently, it is determined whether theheating region A_(i) classified as the recording material central regionAM is an image range on the basis of the image data (image information)(S1005). When the heating region A_(i) is the image range, the heatingregion A_(i) is classified as the image heating region AI (S1006). Whenthe heating region A_(i) is not the image range, the heating regionA_(i) is classified as the non-image heating region AP (S1007). Theclassification of the heating region A_(i) is used for controlling theheat generating quantity of the heat generating block HB_(i), as will bedescribed later. When the heating region A_(i) is classified as theimage heating region AI (S1006), the control temperature TGT_(i) is setas TGT_(i)=T_(AI)−K_(AI) (S1008).

Here, T_(AI) is a reference temperature of the image heating region AI,and is set as a temperature appropriate for fixing a non-fixed image tothe recording material P. When a standard sheet is passed in the fixingapparatus 200 of the present embodiment, T_(AI) is set to 198° C. Thereference temperature T_(AI) of the image heating region AI ispreferably variable according to the type of the recording material P,such as a thick paper or a thin paper. Moreover, the referencetemperature T_(AI) of the image heating region may be adjusted accordingto image information, such as an image density or a pixel density.

Moreover, K_(AI) is a temperature correction term of the image heatingregion AI, and is set according to a heat accumulation count valueCT_(i) in each heating region A_(i) as illustrated in FIG. 8A. Here, theheat accumulation count value CT_(i) is a parameter correlated with aheat accumulation amount of the fixing apparatus 200 in each heatingregion A_(i), and the greater the heat accumulation count value CT_(i),the greater the heat accumulation amount. A method of calculating theheat accumulation count value CT_(i) will be described later.

A heat amount for fixing a toner image to the recording material P,however, is given by the heat generating quantity of the heat generatingblock HB_(i) and the heat accumulation amount in the heating regionA_(i). That is, the greater the heat accumulation amount in the heatingregion A_(i), the more the toner image is likely to be fixed to therecording material P even if the heat generating quantity of the heatgenerating block HB_(i) is small. Therefore, in the image formingapparatus 100 of the present embodiment, the greater the heataccumulation amount (heat accumulation count value CT_(i)), the greaterthe set temperature correction term K_(AI) of the image heating regionAI, so that the control temperature TGT_(i) is decreased and the heatgenerating quantity of the heat generating block HB_(i) is decreased. Bydoing so, an excessive heat amount is prevented from being applied tothe toner image when the heat accumulation amount in the heating regionA_(i) is large, thereby realizing power saving.

Next, a case in which the heating region A_(i) is classified as thenon-image heating region AP (S1007) will be described. When the heatingregion A_(i) is classified as the non-image heating region AP, thecontrol temperature TGT_(i) is set as TGT_(i)=T_(AP)−K_(AP) (S1009).

Here, T_(AP) is a reference temperature of the non-image heating regionAP, and is set as a temperature less than the reference temperatureT_(AI) of the image heating region AI, so that the heat generatingquantity of the heat generating block HB_(i) in the non-image heatingregion AP is less than that of the image heating region AI to realizepower saving of the image forming apparatus 100. If the referencetemperature T_(AP) of the non-image heating region AP is decreased toomuch, however, there may be case in which it is difficult to performheating sufficiently up to the control temperature of the image portioneven if a greatest possible electrical power is supplied to the heatgenerating block HB_(i) when the heating region A_(i) is changed fromthe non-image heating region AP to the image heating region AI. In thiscase, since there is a possibility that a phenomenon (a fixing defect)in which the toner image is not sufficiently fixed to the recordingmaterial P occurs, it is necessary to set the reference temperatureT_(AP) of the non-image heating region AP to an appropriate value.According to the test performed by present inventors, it has found that,in the image forming apparatus 100 of the present embodiment, when thereference temperature T_(AP) of the non-image heating region AP is setto 158° C. or greater, and the heating region A_(i) is changed from thenon-image heating region AP to the image heating region AI, a fixingdefect did not occur. From the viewpoint of power saving, since it ispreferable to decrease the control temperature TGT_(i) as much aspossible to decrease the heat generating quantity of the heat generatingblock HB_(i), T_(AP) is set to 158° C. in the present embodiment. Thereference temperature T_(AP) of the non-image heating region AP ispreferably variable according to the type of the recording material P,such as a thick paper or a thin paper. Moreover, the referencetemperature T_(AP) of the non-image heating region AP may be adjustedaccording to image information, such as an image density or a pixeldensity.

Moreover, K_(AP) is a temperature correction term of the non-imageheating region AP, and as illustrated in FIG. 8B, the greater the heataccumulation count value CT_(i) in each heating region A_(i) (that is,the greater the heat accumulation amount in each heating region A_(i)),the greater the set temperature correction term K_(AP) of the non-imageheating region AP. A heat amount necessary for causing the temperatureof the heater 300 to reach up to the control temperature TGT_(i) of theimage portion when the heating region A_(i) changes, however, from thenon-image heating region AP to the image heating region AI, and is givenby the heat generating quantity of the heat generating block HB_(i) andthe heat accumulation amount in the heating region A_(i). That is, whena largest possible electrical power is supplied to the heat generatingblock HB_(i) (when the supplied electrical power is constant), thegreater the heat accumulation amount in the heating region A_(i), thequicker the temperature of the heater 300 can reach the controltemperature TGT_(i) of the image portion. The expression that thetemperature can reach the control temperature TGT_(i) of the imageportion means that, even if the control temperature TGT_(i) of thenon-image heating region AP is decreased, it is possible to performheating sufficiently up to the control temperature TGT_(i) of the imageportion, and to prevent the occurrence of a fixing defect. Therefore, inthe image forming apparatus 100 of the present embodiment, the greaterthe heat accumulation amount (the heat accumulation count value CT_(i)),the greater the set temperature correction term K_(AP) of the non-imageheating region AP, so that the control temperature TGT_(i) is decreasedand the heat generating quantity of the heat generating block HB_(i) isdecreased. By doing so, an excessive heat amount is prevented from beingapplied to the fixing apparatus 200 when the heat accumulation amount inthe heating region A_(i) is large, thereby realizing power saving.

Next, a case in which the heating region A_(i) is classified as therecording material edge region AE (S1003) will be described. In S1010,it is determined whether a heat accumulation count value CT_(e) (firstcount value) of the recording material edge region AE satisfiesExpression 1 below:CT _(e) <CT _(m) −W _(e)  (Expression 1).CT_(m) is a heat accumulation count value (second count value) of eachheating region A_(i) in the recording material central region AM, andW_(e) is a determination value (predetermined value) for determining theoccurrence of a conveying defect at the recording material edge PE.

Next, S1010 will be described in detail. In S1010, it is determinedwhether the image heating apparatus 200 is in a state in which paperwrinkle as a recording material conveying defect occurs. As describedabove, the heat accumulation count value CT is a parameter correlatedwith the heat accumulation amount of the fixing apparatus 200 in eachheating region, and the greater the heat accumulation count value, thegreater heat accumulation amount. Therefore, the greater the heataccumulation count value CT, the greater the heat accumulation amount ofthe pressure roller 208 that is a fixing member of the image heatingapparatus 200.

The pressure roller 208 has the silicon rubber layer 210 that is anelastic layer formed on the metal core 209 thereof. When the heataccumulation amount is large, the silicon rubber layer thermally expandsand the outer diameter of the pressure roller 208 increases. In thefixing apparatus 200 of the present embodiment, the recording material Pis conveyed according to rotation of the pressure roller 208. Therefore,the greater the heat accumulation count value CT, the more the pressureroller 208 expands, the greater the outer diameter, and the greater theconveying force of the recording material. In this manner, the heataccumulation count value CT is correlated with the conveying force ofthe recording material P.

On the other hand, as means for suppressing a paper wrinkle of arecording material P, the pressure roller 208 of the present embodimentis configured such that the outer diameter at the end thereof is greaterby approximately 100 μm than the outer diameter in the central portionthereof. This is to set the conveying force at the end of the pressureroller 208 to be greater than the conveying force in the centralportion, so as to apply a force of pulling the recording material P fromthe recording material central region toward the recording material edgePE to thereby prevent a paper wrinkle of the recording material P. Forexample, when such an image pattern as illustrated in FIGS. 10A to 10Cis continuously formed, since the heat generating quantity of the imageheating region AI increases, the heat accumulation amount (heataccumulation count value CT_(m)) of the central region is greater thanthe heat accumulation amount (heat accumulation count value CT_(e)) ofthe edge region. Therefore, with a change in the heat accumulationamount, the outer diameter of the pressure roller 208 in the centralregion changes more greatly than the outer diameter of the pressureroller 208 in the edge region. Due to a change in the conveying forceresulting from a change in the heat accumulation amount, the effect ofsuppressing a paper wrinkle of the recording material P by the force ofpulling the recording material P from the recording material centralregion toward the recording material edge PE decreases.

When the heat accumulation count value CT_(e) becomes less than the heataccumulation count value CT_(m) by the determination value W_(e) or morethat is a value for determining the occurrence of a conveying defect atthe recording material edge as illustrated in Expression 1 in S1010 ofthe control flow, a paper wrinkle of the recording material P may occurdue to the above-described change. In the present embodiment, thedetermination value W_(e) is set to 150. The determination value W_(e)is set such that the paper wrinkle of the recording material P is withinan allowable range. The determination value W_(e) is preferably variableaccording to the type (paper weight) of the recording material P, suchas a thick paper or a thin paper. Moreover, the determination valueW_(e) may be adjusted according to a use environment (temperature orhumidity).

When the determination criterion of S1010 is not satisfied (that is, adifference obtained by subtracting the heat accumulation count valueCT_(e) as the first count value from the heat accumulation count valueCT_(m) as the second count value is greater than the determination valueW_(e) as the predetermined value), the flow proceeds to S1005. Moreover,the heating region A_(i) is classified into the image heating region AIand the non-image heating region AP similarly to the recording materialcentral region AM (S1006 and S1007), and the control temperature TGT_(i)is determined according to the classification (S1008 and S1009).

When the determination criterion of S1010 is satisfied (that is, thedifference obtained by subtracting the heat accumulation count valueCT_(e) from the heat accumulation count value CT_(m) is equal to or lessthan the predetermined value (that is, the count value W_(e))), theheating region A_(i) is classified as the recording material edgeheating correction region AW (S1011)). When the heating region A_(i) isclassified as the recording material edge heating correction region AW,the control temperature TGT_(i) is set so that a paper wrinkle does notoccur. In S1012, regardless of whether the image range passes throughthe heating region A_(i), the control temperature TGT_(i) is set asTGT_(i)=T_(AI)−K_(AI) (S1012). T_(AI) is the reference temperature ofthe image heating region AI, and K_(AI) is the temperature correctionterm of the image heating region AI similarly to S1008. In the presentembodiment, when a standard sheet is passed, T_(AI) is set to 198° C.

By the above-described setting, even when such an image as the imagepattern illustrated in FIGS. 10A to 10C does not pass through theheating correction region AW at the edge of the recording material P,heating is performed in a level equivalent to the image heating regionAI of the recording material central region AM. By doing so, it ispossible to suppress an increase in the difference between the edge heataccumulation count value CT_(e) and the central portion heataccumulation count value CT_(m) so as to be maintained within apredetermined range. Therefore, it is possible to maintain a paperwrinkle suppression effect and to prevent the occurrence of a paperwrinkle of a recording material P.

As for the heat generating quantity control temperature TGT_(i) of theheat generating block HB_(i), in an inter-sheet interval when aplurality of images are printed continuously (a segment between apreceding recording material and a subsequent recording material), thecontrol temperature is set as TGT_(i)=T_(AP)−K_(AP) by applying the sameidea as the non-image heating region AP. As for the heat generatingquantity control temperature TGT_(i) of the heat generating block HB_(i)at a post-rotation (an idling segment until the printer enters into aprint standby state after the recording material P at the end ofprinting passed through the heating region A_(i)), the controltemperature is set as TGT_(i)=T_(AP)−K_(AP) by applying the same idea asthe non-image heating region AP.

A method of controlling the heat generating quantity of the heatgenerating block HB_(i) at the time of pre-rotation (startup segment)will be described. Here, the pre-rotation is an idling segment beforethe recording material P at the start of printing reaches the heatingregion A_(i) and is a segment in which control is performed so that thetemperature of the heating region A_(i) reaches a predeterminedtemperature. In the image forming apparatus 100 of the presentembodiment, the control temperature TGT_(i) during a startup operationis given by Expression 2 below:TGT _(i)=(T _(AI) −K _(AI) −T0_(i))÷3×t+T0_(i)  (Expression 2).

In Expression 2, T_(AI) is the reference temperature of the imageheating region AI, and K_(AI) is the temperature correction term of theimage heating region AI. Moreover, t represents the time (seconds)elapsed from the start of a startup operation, and T0_(i) represents thetemperature detected by the thermistor TH corresponding to the heatingregion A_(i) at the start of the startup operation. That is, the controltemperature TGT_(i) is changed linearly from T0_(i) to T_(AI)−K_(AI)every three seconds.

As described above, in the present embodiment, the control temperatureTGT_(i) of the respective heating regions A_(i) is determined accordingto the classification and the heat accumulation count value CT_(i) ofthe heating region A_(i). The setting values of the referencetemperature (T_(AI) and T_(AP)) of each heating region A_(i), thetemperature correction term (K_(AI) and K_(AP)) of each heating regionA_(i), and the determination value W_(e) are to be determinedappropriately by taking the configuration of the image forming apparatus100 and the fixing apparatus 200 and the printing conditions intoconsideration. That is, these values are not limited to theabove-described values.

7. Predicted Heat Accumulation Amount Calculation Method

In the present embodiment, the heat accumulation count value CT_(i) isprovided for respective heating regions A_(i) as a parameter correlatedwith the heat accumulation amount of each heating region A_(i). The heataccumulation count value CT_(i) indicates how much the respectiveheating regions A_(i) are heated and how much heat the respectiveheating regions A_(i) have radiated and is used for predicting the heataccumulation amount by storing and counting the thermal history (heatinghistory and heat radiation history). The heating history can beacquired, for example, on the basis of at least one of a heatertemperature and the amount of electrical power supplied to the heatgenerating element. Moreover, the heat radiation history can beacquired, for example, on the basis of at least one of whether therecording material P has passed through the heating region A_(i), aperiod in which electrical power is not supplied to the heat generatingelement, and a change over time in the heater temperature. dCT_(i),given by Expression 3 below, is accumulated and added to the heataccumulation count value CT_(i) of each heating region A_(i) everypredetermined update timing:dCT _(i)=(TC−RMC−DC)+WUC  (Expression 3).

Here, TC, RMC, DC, and WUC in Expression 3 will be described withreference to FIGS. 9A to 9D. It is assumed that the heat accumulationcount value CT_(i) of the present embodiment is updated every 0.24seconds (every classification segment of the heating region A_(i)) onthe basis of the leading edge of the recording material P as a referenceexcept for the pre-rotation at the start of printing. Moreover, in astandby state in which a printing operation is not performed, the heataccumulation count value CT_(i) is updated every 0.24 seconds on thebasis of the time point at which energization of the heater 300 ended atthe end of the printing operation as a reference.

TC in Expression 3 is a value indicating a heating amount of the heatingregion A_(i) by the heat generating block HB_(i) and is calculated onthe basis of the control temperature of the heater 300 and the amount ofelectrical power supplied to each heat generating element. In Embodiment1, TC is determined according to the control temperature TGT_(i) of eachheating region A_(i) as illustrated in FIG. 9A. The lesser the controltemperature TGT_(i), the lesser the TC value, and the greater thecontrol temperature TGT_(i), the greater the TC value.

RMC in Expression 3 indicates a heat amount deprived from the imageheating apparatus 200 by the recording material P and is set accordingto a passing state (the presence of passing or the like) of therecording material P in each heating region A_(i) as illustrated in FIG.9B. When the recording material P is not present in the heating regionA_(i) (that is, the heating region A_(i) is classified as the heatingregion AN of a non-sheet-passing portion, RMC is set as 0). The RMC maybe variable according to the type of the recording material P, such as athick paper or a thin paper.

DC in Expression 3 indicates the amount of heat radiated outside thefixing apparatus 200 by heat transfer or radiation, and is determinedaccording to the heat accumulation count value CT_(i) of each heatingregion. Since the greater the heat accumulation amount, the greater thetemperature difference from the outside temperature, and the greater theheat radiation amount, the greater the heat accumulation count valueCT_(i), the greater the DC value, as illustrated in FIG. 9C.

Updating of the heat accumulation count value CT_(i) on the basis of TC,RMC, and DC is performed at the CT_(i) update interval of 0.24 secondsin an inter-sheet interval when a plurality of images are printedcontinuously. Moreover, the heat accumulation count value CT_(i) isupdated at the CT_(i) update interval of 0.24 seconds in a standbysegment in which a printing operation is not performed at the time ofpost-rotation at the end of printing. When the inter-sheet interval, thepost-rotation, or the standby segment ends in the middle of the periodof 0.24 seconds, an addition/subtraction amount of TC, RMC, or DC isadjusted. For example, since an inter-sheet interval time in Embodiment1 is 0.12 seconds, which is half the CT_(i) update interval of 0.24seconds, the heat accumulation count value CT_(i) is updated using TC,RMC, and DC, which are half the values illustrated in FIGS. 9A to 9C.Moreover, for example, since the post-rotation time in Embodiment 1 is0.12 seconds similarly to the inter-sheet interval time, the heataccumulation count value CT_(i) is updated using TC, RMC, and DC, whichare half the values illustrated in FIGS. 9A to 9C. Moreover, when theheat accumulation count value CT_(i) obtained as the result of updatingthe heat accumulation count value CT_(i) is smaller than 0, the heataccumulation count value CT_(i) is set to 0.

WUC in Expression 3 indicates an addition amount of the heataccumulation count value CT_(i) at the time of pre-rotation (startupsegment). At the time of pre-rotation, the heat accumulation count valueCT_(i) is not added or subtracted using TC, RMC, and DC. The heataccumulation count value CT_(i) is added using WUC at a time point (aleading edge time point of the recording material P) at which thepre-rotation ends. As illustrated in FIG. 9D, the greater the heataccumulation count value CT_(i), the lesser the set WUC value.

The heat accumulation count value CT_(i) determined in theabove-described manner shows that the greater the heat accumulationcount value CT_(i), the greater the heat accumulation amount in theheating region A_(i). The setting values of TC, RMC, DC, and WUC are tobe determined appropriately by taking the configuration of the imageforming apparatus 100 and the fixing apparatus 200 and the printingconditions into consideration, and are not limited to the valuesillustrated in FIGS. 9A to 9D.

8. Advantages of Present Invention

Advantages of the present embodiment will be described using acomparative example. FIG. 11 illustrates a control flow of thecomparative example. As illustrated in FIG. 11, in the comparativeexample, the heating region A_(i) is classified as either the imageheating region AI or the non-image heating region AP (S1022 to S1024)and the control temperatures TGT_(i) of the respective regions are set(S1025 and S1026). In the comparative example, the control temperaturesTGT_(i) of the image heating region AI and the non-image heating regionAP are set the same as those of Embodiment 1.

Next, the advantages of the present invention will be described by wayof a specific example of Embodiment 1 to be described later as aspecific printing example. In the specific example of Embodiment 1, in astate in which the fixing apparatus 200 is in a room-temperature state(that is, a state in which the heat accumulation count value CT_(i) ofeach heating region A_(i) is 0), 100 pages of a recording material (LTRsize: a sheet width of 216 mm, a sheet length of 279 mm, and a paperweight of 75 g/m²) illustrated in FIGS. 10A to 10C were printedcontinuously. It is assumed that the printed image is disposed in theentire range in which the image passes through the heating regions A₂,A₃, A₄, A₅, and A₆ on the recording material P.

FIG. 12A illustrates a change in the heat accumulation count valueCT_(i) of the heating region A_(i) with respect to the number of passingrecording materials in Embodiment 1.

Moreover, FIG. 12B illustrates a control temperature TGT_(i)corresponding to the number of passing sheets, a heat accumulation countvalue CT_(i), and the occurrence of a paper wrinkle in the printedrecording material P.

In FIG. 12A, a solid line indicates a change in the heat accumulationcount values CT₂ to CT₆ of the heating regions (A₂, A₃, A₄, A₅, and A₆)classified as the recording material central region AM and the imageheating region AI in Embodiment 1. A two-dot chain line indicates achange in the heat accumulation count values CT₁ and CT₇ of the heatingregions (A₁ and A₇) classified as the recording material edge region AEand the non-image heating region AP in Embodiment 1. Moreover, a brokenline indicates a change in the heat accumulation count values CT_(i) andCT₇ of the heating regions A₁ and A₇ in the comparative example. Sincethe heat accumulation count values of the heating regions A₂, A₃, A₄,A₅, and A₆ in the comparative example show the same change as Embodiment1, the description thereof will be omitted.

In the heating regions (A₂, A₃, A₄, A₅, and A₆) classified as therecording material central region AM in Embodiment 1, the heataccumulation count values CT₂ to CT₆ increase as the number of printedpages increases. Since the heating regions (A₂, A₃, A₄, A₅, and A₆) areclassified as the image heating region AI, the temperature T_(AI) of theimage heating region AI is set to 198° C., and the heat accumulationcount values CT₂ to CT₆ of the 39th page reach 185.

Moreover, since the heating regions (A₁ and A₇) classified as therecording material edge region AE are also classified as the non-imageheating region AP, the temperature T_(AP) of the image heating region AIis set to 158° C. Therefore, although the heat accumulation count valuesCT₁ and CT₇ increase as the number of printed pages increases, since theheat generating quantity of the heat generating block HB_(i) isdecreased, the heat accumulation count values CT₁ and CT₇ do notincrease to be greater than the heat accumulation count values CT₂ toCT₆ of the recording material central region AM. The heat accumulationcount values CT₁ and CT₇ of the 39th page reach 33. As described above,the determination value W_(e) is set to 150. Therefore, the condition ofExpression 1 illustrated in S1010 of the control flow of FIG. 6 issatisfied when the number of passing sheets reaches 39. Therefore, theheating regions (A₁ and A₇) in the 39th and subsequent pages areclassified as the heating correction region AW of the recording materialedge and the control temperature TGT_(i) is set asTGT_(i)=T_(AI)−K_(AI). The control temperature TGT_(i) is set to 198° C.

As illustrated in FIG. 12A, for the 39th and subsequent pages, the heataccumulation count values CT₁ and CT₇ increase substantially similarlyto the heat accumulation count values CT₂ to CT₆ corresponding to therecording material central region AM. Therefore, as illustrated in FIG.12B, the difference in the heat accumulation count value of therecording material edge region AE and the recording material centralregion AM is maintained to approximately 150 and is maintained within apredetermined range without increasing to a certain level or higher.

Although the pressure roller 208 of the present embodiment is configuredsuch that the outer diameter at the ends is greater by approximately 100m than the outer diameter at the central portion, a paper wrinkle can besuppressed when the outer diameter difference is maintained to 70 μm ormore. Although the heat accumulation count value CT_(i) is a parametercorrelated with the outer diameter of the pressure roller 208, the heataccumulation count value difference of 150 corresponds to a pressureroller outer diameter difference of 30 μm. Therefore, in such a printingexample as the specific example of Embodiment 1, although the pressureroller outer diameter difference decreases, the outer diameterdifference can be maintained to 70 μm or more. Therefore, in Embodiment1, the pressure roller outer diameter difference in the recordingmaterial edge region AE and the recording material central region AM canbe maintained within a certain range and the occurrence of a paperwrinkle can be suppressed.

In the comparative example, as illustrated in FIGS. 12A and 12C, adifference in the heat accumulation amount of the recording materialedge region AE and the recording material central region AM increases asthe number of passing sheets increases and reaches 231 when the numberof passing sheets reaches 70. Therefore, in the comparative example, theouter diameter difference at the central portion and the end of thepressure roller decreases up to 60 μm or less when the number of passingsheets reaches 70. Therefore, the pressure roller outer diameter in therecording material central region AM becomes greater by a predeterminedrange or more than the outer diameter in the recording material edgeregion AE and a paper wrinkle suppression effect decreases. As a result,a paper wrinkle occurs.

As described above, in the present embodiment, the difference in theheat accumulation amount of the recording material edge region AE andthe recording material central region AM does not increase up to acertain level or more. Therefore, it is possible to maintain the outerdiameter difference of the pressure roller to be within a certain rangeand to suppress the occurrence of a paper wrinkle. Moreover, by changingthe control temperature TGT_(i) between the image heating region AI andthe non-image heating region AP, it is possible to decrease the heatgenerating quantity of the non-image heating region AP and to achievepower saving.

In the present embodiment, a heating region of the heat generatingelement disposed at the first stage in the longitudinal direction of theplurality of heat generating elements is determined as the recordingmaterial edge region AE, and a heating region of the heat generatingelement other than the heat generating element is determined as therecording material central region AM. The present invention is notlimited, however, to such a configuration. That is, depending on thecorrespondence between the number of arranged heat generating elementsand the size in the longitudinal direction of the recording material, aheating region of a heat generating element disposed on the inner sidethan the first stage may be determined as the recording material edgeregion AE. In this case, a heating region of a heat generating elementdisposed on the inner side in the longitudinal direction than the heatgenerating element, the heating region of which is determined as therecording material edge region AE, is determined as the recordingmaterial central region AM.

Embodiment 2

Embodiment 2 of the present invention will be described. In Embodiment2, the heat accumulation count values CT that indicate the thermalhistory between the recording material edge region AE and the recordingmaterial central region AM are compared, and the control temperature ofthe image heating region AI and the control temperature of the non-imageheating region AP in the recording material edge region are changedaccording to the comparison result using a paper wrinkle correctionterm. A basic configuration and operations of the image formingapparatus 100 and the image heating apparatus 200 of Embodiment 2 arethe same as those of Embodiment 1. Therefore, elements of Embodiment 2having the same or corresponding function and configuration as those ofEmbodiment 1 are denoted by the same reference numerals and thedescription thereof will be omitted. Matters that are not particularlydescribed in Embodiment 2 are similar to those of Embodiment 1.

FIG. 13A is a flowchart for determining a classification and a controltemperature of a heating region A_(i) according to Embodiment 2. FIGS.13B and 13C illustrate setting values of parameters associated with thecontrol temperature according to Embodiment 2. As illustrated in theflowcharts of FIG. 13A, each of the heating regions A_(i) (i=1 to 7) isclassified into a recording material edge region AE, a recordingmaterial central region AM, an image heating region AI, and a non-imageheating region AP. The heating region A_(i) is classified on the basisof image data (image information) and recording material information (arecording material size) sent from an external apparatus (notillustrated), such as a host computer.

That is, on the basis of the size information of a recording material P,it is determined whether the heating region A_(i) is a region throughwhich the recording material edge PE passes or a region through which aregion other than the recording material edge passes (S1032). When therecording material edge PE passes through the heating region A_(i), theheating region A_(i) is classified as the recording material edge regionAE (S1033). When the recording material central portion other than therecording material edge PE passes through the heating region A_(i), theheating region A_(i) is classified as the recording material centralregion AM (S1034). Subsequently, it is determined whether the heatingregion A_(i) classified as the recording material central region AM isan image range on the basis of the image data (image information)(S1035). When the heating region A_(i) is the image range, the heatingregion A_(i) is classified as the image heating region AI (S1036). Whenthe heating region A_(i) is not the image range, the heating regionA_(i) is classified as the non-image heating region AP (S1037). Theclassification of the heating region A_(i) is used for controlling theheat generating quantity of the heat generating block HB_(i), as will bedescribed later.

When the heating region A_(i) is classified as the image heating regionAI (S1036), the control temperature TGT_(i) is set asTGT_(i)=T_(AI)−K_(AI) (S1038). When a standard sheet is passed in thefixing apparatus 200 of the present embodiment, T_(AI) is set to 198° C.

Next, a case in which the heating region A_(i) is classified as thenon-image heating region AP (S1037) will be described. When the heatingregion A_(i) is classified as the non-image heating region AP, thecontrol temperature TGT_(i) is set as TGT_(i)=T_(AP)−K_(AP) (S1039).

Here, T_(AP) is a reference temperature of the non-image heating regionAP and is set as a temperature less than the reference temperatureT_(AI) of the image heating region AI so that the heat generatingquantity of the heat generating block HB_(i) in the non-image heatingregion AP is less than that of the image heating region AI to realizepower saving of the image forming apparatus 100. In the presentembodiment, T_(AP) is set as 158° C. The reference temperature T_(AI) ofthe image heating region AI and the reference temperature T_(AP) of thenon-image heating region AP are preferably variable according to thetype of the recording material P, such as a thick paper or a thin paper.Moreover, the reference temperature may be adjusted according to imageinformation such as an image density or a pixel density.

Moreover, the temperature correction term K_(AI) of the image heatingregion AI and the temperature correction term K_(AP) of the non-imageheating region AP are set according to the heat accumulation count valueCT_(i) in each heating region A_(i) as illustrated in FIG. 8A, similarlyto Embodiment 1.

Next, a case in which the heating region A_(i) is classified as therecording material edge region AE (S1033) will be described. In S1040,it is determined whether a heat accumulation count value CT_(e) of therecording material edge region AE satisfies Expression 1 below:CT _(e) <CT _(m) −W _(e)  (Expression 1).

CT_(m) is a heat accumulation count value of each heating region A_(i)in the recording material central region AM, and W_(e) is adetermination value for determining occurrence of a conveying defect atthe recording material edge.

Next, S1040 will be described in detail.

In S1040, it is determined whether the image heating apparatus 200 is ina state in which paper wrinkle as a recording material conveying defectoccurs. As described above, the heat accumulation count value CT is aparameter correlated with the heat accumulation amount of the fixingapparatus 200 in each heating region A_(i), and the greater the heataccumulation count value CT, the greater heat accumulation amount.Therefore, the greater the heat accumulation count value CT, the greaterthe heat accumulation amount of the pressure roller 208 as a fixingmember of the image heating apparatus 200. Therefore, the greater theheat accumulation count value CT, the more the outer diameter of thepressure roller 208 is expanded, and the greater the recording materialconveying force. As described above, the heat accumulation count valueCT is a parameter correlated with the recording material conveyingforce.

When the heat accumulation count value CT_(e) becomes less than the heataccumulation count value CT_(m) by the determination value W_(e) ormore, as illustrated in Expression 1 in S1040 of the control flow, apaper wrinkle of the recording material P may occur due to theabove-described change. In the present embodiment, the determinationvalue W_(e) is set to 150. The determination value W_(e) is preferablyvariable according to the type (paper weight) of the recording materialP, such as a thick paper or a thin paper. Moreover, the determinationvalue W_(e) may be adjusted according to a use environment (temperatureor humidity).

First, when the determination criterion of S1040 is not satisfied, it isdetermined that the difference in the heat accumulation amount of thepressure roller 208 is within a predetermined range and a paper wrinkleof the recording material P resulting from a change in the outerdiameter of the pressure roller does not occur, and the flow proceeds toS1035. Moreover, the heating region A_(i) is classified into the imageheating region AI and the non-image heating region AP similarly to therecording material central region AM (S1036 and S1037), and the controltemperature is determined according to the classification (S1038 andS1039).

When the determination criterion of S1040 is satisfied, it is determinedthat a paper wrinkle of the recording material P resulting from a changein the outer diameter of the pressure roller may occur if the differencein the heat accumulation amount of the pressure roller 208 increasesfurther, and the control temperature of the heat generating block iscontrolled to the control temperature TGT_(e) for paper wrinklecorrection. First, it is determined whether the heating region A_(i) isan image range on the basis of the image data (image information)(S1041). When the heating region A_(i) is the image range, the heatingregion A_(i) is classified as the image heating region AI (S1042). Whenthe heating region A_(i) is not the image range, the heating regionA_(i) is classified as the non-image heating region AP (S1043). Theclassification of the heating region A_(i) is used for controlling theheat generating quantity of the heat generating block HB_(i), as will bedescribed later.

When the heating region A_(i) is classified as the image heating regionAI (S1042), the control temperature is set asTGT_(e)=T_(AI)−K_(Ai)+W_(AI) (S1044).

Here, T_(AI) is a reference temperature of the image heating region AIand is set as a temperature appropriate for fixing a non-fixed image tothe recording material P. When a standard sheet is passed in the fixingapparatus 200 of the present embodiment, T_(AI) is set to 198° C.

Moreover, K_(AI) is a temperature correction term of the image heatingregion AI and is set according to a heat accumulation count value CT_(i)in each heating region A_(i) as illustrated in FIG. 8A.

Moreover, W_(AI) is a paper wrinkle correction term of the image heatingregion AI and is set as illustrated in FIG. 13B.

Next, a case in which the heating region A_(i) is classified as thenon-image heating region AP (S1043) will be described. When the heatingregion A_(i) is classified as the non-image heating region AP, thecontrol temperature is set as TGT_(e)=T_(AP)−K_(AP)+W_(AP) (S1045).Here, T_(AP) is a reference temperature of the non-image heating regionAP and is set as a temperature appropriate for fixing a non-fixed imageto the recording material P. When a standard sheet is passed in thefixing apparatus 200 of the present embodiment, T_(AP) is set to 158° C.

Moreover, K_(AP) is a temperature correction term of the non-imageheating region AP and is set according to the heat accumulation countvalue CT_(i) in each heating region A_(i), as illustrated in FIG. 8B.

Moreover, W_(AP) is a paper wrinkle correction term of the non-imageheating region AP and is set as illustrated in FIG. 13C.

For example, in a state in which the heat accumulation count valueCT_(i) is 100 or less, the control temperature of the non-image heatingregion AP is set as TGT_(e)=193° C.

By the above-described control flow, even when such an image as theimage pattern illustrated in FIGS. 10A to 10C does not pass through theedge region, heating is performed in a level equivalent to the imageheating region AI of the recording material central region AM. By doingso, it is possible to suppress an increase in the difference between theedge heat accumulation count value CT_(e) and the central portion heataccumulation count value CT_(m). Moreover, in the present embodiment,even when an image passes through the edge region, it is possible tosuppress an increase in the difference between the edge heataccumulation count value CT_(e) and the central portion heataccumulation count value CT_(m). Therefore, it is possible to maintain apaper wrinkle suppression effect and to prevent the occurrence of apaper wrinkle of a recording material P.

The setting values of the reference temperature (T_(AI) and T_(AP)) ofeach heating region A_(i), the temperature correction term (K_(AI) andK_(AP)) of each heating region A_(i), the paper wrinkle correction term(W_(AI) and W_(AP)), and the determination value W_(e) for a conveyingdefect at the edges of the recording material P are determinedappropriately by taking the configuration of the image forming apparatus100 and the fixing apparatus 200 and the printing conditions intoconsideration. These values are not limited, however, to theabove-described values.

Next, the advantages of Embodiment 2 will be described by way of aheater control method using a comparative example and a specific exampleof Embodiment 2 to be described later will be described as a specificprinting example. In the specific example of Embodiment 2, in a state inwhich the fixing apparatus 200 is in a room-temperature state (that is,a state in which the heat accumulation count value CT_(i) of eachheating region A_(i) is 0), 100 pages of a recording material Pillustrated in FIGS. 10A to 10C were printed continuously. FIG. 14Aillustrates a change in the heat accumulation count value CT_(i) of theheating region A_(i) with respect to the number of passing recordingmaterials in Embodiment 2.

Moreover, FIG. 14B illustrates a control temperature corresponding tothe number of passing sheets, a heat accumulation count value, and theoccurrence of a paper wrinkle in the printed recording material.

In FIG. 14A, a solid line indicates a change in the heat accumulationcount values CT₂ to CT₆ of the heating regions (A₂, A₃, A₄, A₅, and A₆)classified as the recording material central region AM and the imageheating region AI in Embodiment 2. A two-dot chain line indicates achange in the heat accumulation count values CT₁ and CT₇ of the heatingregions (A₁ and A₇) classified as the recording material edge region AEand the non-image heating region AP in Embodiment 2. Moreover, a brokenline indicates a change in the heat accumulation count values CT₁ andCT₇ of the heating regions A₁ and A₇ in the comparative example. Sincethe heat accumulation count values of the heating regions A₂, A₃, A₄,A₅, and A₆ in the comparative example show the same change as Embodiment2, the description thereof will be omitted.

In the heating regions (A₂, A₃, A₄, A₅, and A₆) classified as therecording material central region AM in Embodiment 2, the heataccumulation count values CT₂ to CT₆ increase as the number of printedpages increases. Since the heating regions (A₂, A₃, A₄, A₅, and A₆) areclassified as the image heating region AI, the temperature T_(AI) of theimage heating region AI is set to 198° C., and the heat accumulationcount values CT₂ to CT₆ of the 39th page reach 185.

Moreover, since the heating regions (A₁ and A₇) classified as therecording material edge region AE is classified as the non-image heatingregion AP, the temperature T_(AP) of the image heating region AI is setto 158° C. Therefore, although the heat accumulation count values CT₁and CT₇ increase as the number of printed pages increases, since theheat generating quantity of the heat generating block HB_(i) isdecreased, the heat accumulation count values CT₁ and CT₇ do notincrease to be greater than the heat accumulation count values CT₂ toCT₆ of the recording material central region AM. The heat accumulationcount values CT₁ and CT₇ of the 39th page reach 33. As described above,the determination value W_(e) is set to 150. Therefore, the condition ofExpression 1 illustrated in S1040 of the control flow of FIG. 13A issatisfied when the number of passing sheets reaches 39. Therefore, thecontrol temperature of the heating regions (A₁ and A₇) in the 39th andsubsequent pages is set as TGT_(e)=T_(AI)−K_(Ai)+W_(AP). The controltemperature TGT_(i) is set to 193° C.

For the 39th and subsequent pages, the heat accumulation count valuesCT₁ and CT₇ increase as illustrated in FIG. 14A, and the difference inthe heat accumulation count value of the recording material edge regionAE and the recording material central region AM is maintained toapproximately 150 without increasing to a certain level or higher asillustrated in FIG. 14B. As described above, although the pressureroller 208 of the present embodiment is configured such that the outerdiameter at the ends is greater by approximately 100 μm than the outerdiameter at the central portion, a paper wrinkle can be suppressed whenthe outer diameter difference is maintained to 70 μm or more. Althoughthe heat accumulation count value is a parameter correlated with theouter diameter of the pressure roller 208, the heat accumulation countvalue difference of 150 corresponds to a pressure roller outer diameterdifference of 30 μm. Therefore, in such a printing example as thespecific example of Embodiment 2, although the pressure roller outerdiameter difference decreases, the outer diameter difference can bemaintained to 70 μm or more. Therefore, in Embodiment 2, the pressureroller outer diameter difference in the recording material edge regionAE and the recording material central region AM can be maintained withina certain range and the occurrence of a paper wrinkle can be suppressed.

In the comparative example, as illustrated in FIGS. 14A and 14C, adifference in the heat accumulation amount of the recording materialedge region AE and the recording material central region AM increases asthe number of passing sheets increases and reaches 231 when the numberof passing sheets reaches 70. Therefore, in the comparative example, theouter diameter difference at the central portion and the end of thepressure roller decreases up to 60 μm or less when the number of passingsheets reaches 70. Therefore, the pressure roller outer diameter in therecording material central region AM becomes greater than the outerdiameter in the recording material edge region AE and a paper wrinklesuppression effect decreases. As a result, a paper wrinkle occurs.

As described above, in the present embodiment, the difference in theheat accumulation amount of the recording material edge region AE andthe recording material central region AM does not increase up to acertain level or more. Therefore, it is possible to maintain the outerdiameter difference of the pressure roller 208 to be within a certainrange and to suppress the occurrence of a paper wrinkle. Moreover,regardless of the presence of an image in the recording material edgeregion AE, it is possible to suppress a difference in the heataccumulation amount and to suppress a paper wrinkle more stably.Moreover, by changing the control temperature TGT_(i) between the imageheating region AI and the non-image heating region AP, it is possible todecrease the heat generating quantity of the non-image heating region APand to achieve power saving.

Embodiment 3

Embodiment 3 of the present invention will be described. In Embodiment3, the heat accumulation count values CT indicating the thermal historybetween the recording material edge region AE and the recording materialcentral region AM are compared, and the control temperature of the imageheating region AI and the control temperature of the non-image heatingregion AP in the recording material edge region AE are changed accordingto the comparison result using a paper conveying defect correction term.A basic configuration and operations of the image forming apparatus 100and the image heating apparatus 200 of Embodiment 3 are the same asthose of Embodiment 1. Therefore, elements of Embodiment 3 having thesame or corresponding function and configuration as those of Embodiment1 are denoted by the same reference numerals and the description thereofwill be omitted. Matters that are not particularly described inEmbodiment 3 are similar to those of Embodiment 1.

FIG. 15A is a flowchart for determining a classification and a controltemperature of a heating region A_(i) according to Embodiment 3. FIGS.15B and 15C illustrate setting values of parameters associated with thecontrol temperature according to Embodiment 3. As illustrated in theflowchart of FIG. 15A, each of the heating regions A_(i) (i=1 to 7) isclassified into a recording material edge region AE, a recordingmaterial central region AM, an image heating region AI, and a non-imageheating region AP. The heating region A_(i) is classified on the basisof image data (image information) and recording material information (arecording material size) sent from an external apparatus (notillustrated), such as a host computer.

That is, on the basis of the size information of a recording material P,it is determined whether the heating region A_(i) is a region throughwhich the recording material edge PE passes or a region through which aregion other than the recording material edge passes (S1052). When therecording material edge PE passes through the heating region A_(i), theheating region A_(i) is classified as the recording material edge regionAE (S1053). When the recording material central portion other than therecording material edge PE passes through the heating region A_(i), theheating region A_(i) is classified as the recording material centralregion AM (S1054). Subsequently, it is determined whether the heatingregion A_(i) classified as the recording material edge region AE is animage range on the basis of the image data (image information) (S1055).When the heating region A_(i) is the image range, the heating regionA_(i) is classified as the image heating region AI (S1056). When theheating region A_(i) is not the image range, the heating region A_(i) isclassified as the non-image heating region AP (S1057). Theclassification of the heating region A_(i) is used for controlling theheat generating quantity of the heat generating block HB_(i) as will bedescribed later.

When the heating region A_(i) is classified as the image heating regionAI (S1056), the control temperature TGT_(i) is set asTGT_(i)=T_(AI)−K_(AI) (S1058). When a standard sheet is passed in thefixing apparatus 200 of the present embodiment, T_(AI) is set to 198° C.

Next, a case in which the heating region A_(i) is classified as thenon-image heating region AP (S1057) will be described. When the heatingregion A_(i) is classified as the non-image heating region AP, thecontrol temperature TGT_(i) is set as TGT_(i)=T_(AP)−K_(AP) (S1059).

Here, T_(AP) is a reference temperature of the non-image heating regionAP, and is set as a temperature less than the reference temperatureT_(AI) of the image heating region AI, so that the heat generatingquantity of the heat generating block HB_(i) in the non-image heatingregion AP is less than that of the image heating region AI to realizepower saving of the image forming apparatus 100. In the presentembodiment, T_(AP) is set as 158° C. The reference temperature T_(AI) ofthe image heating region AI and the reference temperature T_(AP) of thenon-image heating region AP are preferably variable according to thetype of the recording material P, such as a thick paper or a thin paper.Moreover, the reference temperature may be adjusted according to imageinformation such as an image density or a pixel density.

Moreover, the temperature correction term K_(AI) of the image heatingregion AI and the temperature correction term K_(AP) of the non-imageheating region AP are set according to the heat accumulation count valueCT_(i) in each heating region A_(i) as illustrated in FIG. 8A similarlyto Embodiment 1.

Next, a case in which the heating region A_(i) is classified as therecording material central region AM (S1054) will be described. InS1060, it is determined whether a heat accumulation count value CT_(m)of the recording material central region AM satisfies Expression 4below:CT _(m) <CT _(e) −X _(e)  (Expression 4).

CT_(e) is a heat accumulation count value of each heating region A_(i)in the recording material edge region AE, and X_(e) is a determinationvalue for determining a recording material conveying defect.

Next, S1060 will be described in detail.

In S1060, it is determined whether the image heating apparatus 200 is ina state in which a recording material trailing edge pop-up as arecording material conveying defect occurs. A recording materialtrailing edge pop-up is a phenomenon in which a trailing edge of arecording material in the conveying direction pops up toward an imagesurface on an upstream side of the image heating apparatus 200, and is aphenomenon in which the trailing edge makes contact with a constituentmember of the image forming apparatus 100 to cause an image defect. Asdescribed above, the heat accumulation count value CT is a parametercorrelated with the heat accumulation amount of the fixing apparatus 200in each heating region A_(i), and the greater the heat accumulationcount value, the greater the heat accumulation amount. Therefore, thegreater the heat accumulation count value CT, the greater the heataccumulation amount of the pressure roller 208 that is a fixing memberof the image heating apparatus 200. Therefore, the greater the heataccumulation count value CT, the more the outer diameter of the pressureroller is expanded, and the greater the recording material conveyingforce. As described above, the heat accumulation count value CT is aparameter correlated with the recording material conveying force.

When the heat accumulation count value CT_(m) given by Expression 4 inS1060 of the control flow becomes less than the heat accumulation countvalue CT_(e) by the determination value X_(e) or more, an image defectresulting from a trailing edge pop-up may occur due to theabove-described change. In the present embodiment, the determinationvalue X_(e) is set to 150. The determination value X_(e) is preferablyvariable according to the type (paper weight) of the recording materialP, such as a thick paper or a thin paper. Moreover, the determinationvalue X_(e) may be adjusted according to a use environment (temperatureor humidity).

First, when the determination criterion of S1060 is not satisfied, it isdetermined that the difference in the heat accumulation amount of thepressure roller 208 is within a predetermined range, and a trailing edgepop-up of the recording material resulting from a change in the outerdiameter of the pressure roller does not occur, and the flow proceeds toS1055. Moreover, the heating region A_(i) is classified into the imageheating region AI and the non-image heating region AP similarly to therecording material edge region AE (S1056 and S1057), and the controltemperature is determined according to the classification (S1058 andS1059).

When the determination criterion of S1060 is satisfied, it is determinedthat a trailing edge pop-up of the recording material resulting from achange in the outer diameter of the pressure roller may occur if thedifference in the heat accumulation amount of the pressure roller 208increases further, and the control temperature of the heat generatingblock is controlled to the control temperature TGT_(m) for paperconveyance correction. First, it is determined whether the heatingregion A_(i) is an image range on the basis of the image data (imageinformation) (S1061). When the heating region A_(i) is the image range,the heating region A_(i) is classified as the image heating region AI(S1062). When the heating region A_(i) is not the image range, theheating region A_(i) is classified as the non-image heating region AP(S1063). The classification of the heating region A_(i) is used forcontrolling the heat generating quantity of the heat generating blockHB_(i) as will be described later.

When the heating region A_(i) is classified as the image heating regionAI (S1062), the control temperature is set asTGT_(e)=T_(AI)−K_(Ai)+X_(AI) (S1064).

Here, T_(AI) is a reference temperature of the image heating region AI,and is set as a temperature appropriate for fixing a non-fixed image tothe recording material P. When a standard sheet is passed in the fixingapparatus 200 of the present embodiment, T_(AI) is set to 198° C.

Moreover, K_(AI) is a temperature correction term of the image heatingregion AI, and is set according to a heat accumulation count valueCT_(i) in each heating region A_(i) as illustrated in FIG. 8A.

Moreover, X_(AI) is a paper conveyance correction term of the imageheating region AI, and is set as illustrated in FIG. 15B.

Next, a case in which the heating region A_(i) is classified as thenon-image heating region AP (S1063) will be described. When the heatingregion A_(i) is classified as the non-image heating region AP, thecontrol temperature is set as TGT_(m)=T_(AP)−K_(AP)+X_(AP) (S1065).Here, T_(AP) is a reference temperature of the non-image heating regionAP, and is set as a temperature appropriate for fixing a non-fixed imageto the recording material P. When a standard sheet is passed in thefixing apparatus 200 of the present embodiment, T_(AP) is set to 158° C.

Moreover, K_(AP) is a temperature correction term of the non-imageheating region AP, and is set according to the heat accumulation countvalue CT_(i) in each heating region A_(i) as illustrated in FIG. 8B.

Moreover, X_(AP) is a paper wrinkle correction term of the non-imageheating region AP, and is set as illustrated in FIG. 15C.

For example, in a state in which the heat accumulation count valueCT_(i) is 100 or less, the control temperature of the non-image heatingregion AP is set as TGT=193° C.

By the above-described control flow, even when such an image as theimage pattern illustrated in FIGS. 16A and 16B does not pass through thecentral region, heating is performed in a level equivalent to the imageheating region AI of the recording material edge region AE. By doing so,it is possible to suppress an increase in the difference between theedge heat accumulation count value CT_(e) and the central portion heataccumulation count value CT_(m). Moreover, even when an image passesthrough the central region, it is possible to suppress an increase inthe difference between the edge heat accumulation count value CT_(e) andthe central portion heat accumulation count value CT_(m) and to maintainthe difference to be within a predetermined range. In this way, it ispossible to prevent the occurrence of a trailing edge pop-up of arecording material.

The setting values of the reference temperature (T_(AI) and T_(AP)) ofeach heating region A_(i), the temperature correction term (K_(AI) andK_(AP)) of each heating region A_(i), the conveying defect correctionterm (X_(AI) and X_(AP)), and the determination value X_(e) for aconveying defect of the recording material are determined appropriatelyby taking the configuration of the image forming apparatus 100 and thefixing apparatus 200 and the printing conditions into consideration.These values are not limited, however, to the above-described values.

Next, the advantages of Embodiment 3 will be described by way of aheater control method using a comparative example, and a specificexample of Embodiment 3 to be described later will be described as aspecific printing example. In the specific example of Embodiment 3, in astate in which the fixing apparatus 200 is in a room-temperature state(that is, a state in which the heat accumulation count value CT_(i) ofeach heating region A_(i) is 0), 100 pages of a recording material Pillustrated in FIGS. 16A and 16B were printed continuously. FIG. 17Aillustrates a change in the heat accumulation count value CT_(i) of theheating region A_(i) with respect to the number of passing recordingmaterials in Embodiment 3.

Moreover, FIG. 17B illustrates a control temperature corresponding tothe number of passing sheets, a heat accumulation count value, and theoccurrence of an image defect resulting from a trailing edge pop-up inthe printed recording material P.

In FIG. 17A, a solid line indicates a change in the heat accumulationcount values CT₁ and CT₇ of the heating regions (A₁ and A₇) classifiedas the recording material edge region AE and the image heating region AIin Embodiment 3. A two-dot chain line indicates a change in the heataccumulation count values CT₂ to CT₆ of the heating regions (A₂, A₃, A₄,A₅, and A₆) classified as the recording material central region AM andthe non-image heating region AP in Embodiment 3. Moreover, a broken lineindicates a change in the heat accumulation count values CT₂ to CT₆ ofthe heating regions (A₂, A₃, A₄, A₅, and A₆) in the comparative example.Since the heat accumulation count values of the heating regions A₁, andA₇ in the comparative example show the same change as Embodiment 3, thedescription thereof will be omitted.

In the heating regions (A₁ and A₇) classified as the recording materialedge region AE in Embodiment 3, the heat accumulation count values CT₁and CT₇ increase as the number of printed pages increases. Since theheating regions (A₁ and A₇) are classified as the image heating regionAI, the temperature T_(AI) of the image heating region is set to 198°C., and the heat accumulation count values CT₁ and CT₇ of the 39th pagereach 185.

Moreover, since the heating regions (A₂, A₃, A₄, A₅, and A₆) classifiedas the recording material central region AM are classified as thenon-image heating region AP, the temperature T_(AP) of the image heatingregion AI is set to 158° C. Therefore, although the heat accumulationcount values CT₂ to CT₆ increase as the number of printed pagesincreases, since the heat generating quantity of the heat generatingblock HB_(i) is decreased, the heat accumulation count values CT₂ to CT₆do not increase to be greater than the heat accumulation count valuesCT₁ and CT₇ of the recording material edge region AE. The heataccumulation count values CT₂ to CT₆ of the 39th page reach 33. Asdescribed above, the determination value X_(e) is set to 150. Therefore,the condition of Expression 4 illustrated in S1060 of the control flowof FIG. 15A is satisfied when the number of passing sheets reaches 39.Therefore, the control temperature of the heating regions (A₂ to A₆) inthe 39th and subsequent pages is set as TGT_(m)=T_(AP)−K_(AP)+X_(AP).The control temperature TGT_(m) is set to 203° C.

For the 39th and subsequent pages, the heat accumulation count valuesCT₂ to CT₆ increase as illustrated in FIG. 17A, and the difference inthe heat accumulation count value of the recording material edge regionAE and the recording material central region AM is maintained toapproximately 150 without increasing to a certain level or higher, asillustrated in FIG. 17B. As described above, although the pressureroller 208 of the present embodiment is configured such that the outerdiameter at the ends is greater by approximately 100 μm than the outerdiameter at the central portion, a trailing edge pop-up can besuppressed when the outer diameter difference is maintained to 130 μm orsmaller. Although the heat accumulation count value CT_(i) is aparameter correlated with the outer diameter of the pressure roller, theheat accumulation count value difference of 150 corresponds to apressure roller outer diameter difference of 30 μm. Therefore, in such aprinting example as the specific example of Embodiment 3, although thepressure roller outer diameter difference decreases, the outer diameterdifference can be maintained to 130 μm or smaller. Therefore, inEmbodiment 3, the pressure roller outer diameter difference in therecording material edge region AE and the recording material centralregion AM can be maintained within a certain range, and the occurrenceof a trailing edge pop-up can be suppressed.

In the comparative example, as illustrated in FIGS. 17A and 17C, adifference in the heat accumulation amount of the recording materialedge region AE and the recording material central region AM increases asthe number of passing sheets increases, and reaches 231 when the numberof passing sheets reaches 70. Therefore, in the comparative example, theouter diameter difference at the central portion and the end of thepressure roller decreases up to 140 μm or more when the number ofpassing sheets reaches 70. Therefore, the pressure roller outer diameterin the recording material edge region AE becomes greater than the outerdiameter in the recording material central region AM. Since a differencein the recording material conveying force increases when the outerdiameter difference between the central portion and the end of thepressure roller increases, the recording material P receives a largeforce that spreads the recording material P in the direction of theedges PE in the width direction (the direction orthogonal to theconveying direction of the recording material). Therefore, the recordingmaterial P pops up toward the image surface after the trailing edgeslips out of the transfer roller 20.

As described above, in the present embodiment, the difference in theheat accumulation amount of the recording material edge region AE andthe recording material central region AM does not increase up to acertain level or more. Therefore, it is possible to maintain the outerdiameter difference of the pressure roller to be within a certain rangeand to suppress the occurrence of a trailing edge pop-up. Moreover,regardless of the presence of an image in the recording material edgeregion AE, it is possible to suppress a difference in the heataccumulation amount and to suppress a trailing edge pop-up more stably.Moreover, by changing the control temperature TGT_(i) between the imageheating region AI and the non-image heating region AP, it is possible todecrease the heat generating quantity of the non-image heating region APand to achieve power saving.

Embodiment 4

Embodiment 4 of the present invention will be described. In Embodiment4, the heat accumulation count values CT indicating the thermal historybetween the heating regions A_(i) at symmetric positions in relation tothe central position of the image heating apparatus 200 in the directionorthogonal to the conveying direction of the recording material arecompared, and the control temperature of the image heating region AI andthe control temperature of the non-image heating region AP are changedaccording to the comparison result. A basic configuration and operationsof the image forming apparatus 100 and the image heating apparatus 200of Embodiment 4 are the same as those of Embodiment 1. Therefore,elements of Embodiment 4 having the same or corresponding function andconfiguration as those of Embodiment 1 are denoted by the same referencenumerals and the description thereof will be omitted. Matters that arenot particularly described in Embodiment 4 are similar to those ofEmbodiment 1.

FIG. 18 is a flowchart for determining a classification and a controltemperature of a heating region A_(i) according to Embodiment 4. Theheating region A_(i) is classified on the basis of image data (imageinformation) sent from an external apparatus (not illustrated), such asa host computer. That is, it is determined whether the heating regionA_(i) is an image range on the basis of the image information (S1072).When the heating region A_(i) is the image range, the heating regionA_(i) is classified as the image heating region AI (S1073). When theheating region A_(i) is not the image range, the heating region A_(i) isclassified as the non-image heating region AP (S1074). Theclassification of the heating region A_(i) is used for controlling theheat generating quantity of the heat generating block HB_(i), as will bedescribed later.

Next, a heater control method according to the present embodiment (thatis, a method of controlling the heat generating quantity of the heatgenerating block HB_(i) (i=1 to 7)) will be described. When the heatingregion A_(i) is classified as the image heating region AI (S1073), thecontrol temperature TGT_(i) is set as TGT_(i)=T_(AI)−K_(AI) (S1075).When a standard sheet is passed in the fixing apparatus 200 of thepresent embodiment, T_(AI) is set to 198° C. Next, a case in which theheating region A_(i) is classified as the non-image heating region AP(S1074) will be described. When the heating region A_(i) is classifiedas the non-image heating region AP, the control temperature TGT_(i) isset as TGT_(i)=T_(AP)−K_(AP) (S1076).

Here, T_(AP) is a reference temperature of the non-image heating regionAP, and is set as a temperature that is less than the referencetemperature T_(AI) of the image heating region so that the heatgenerating quantity of the heat generating block HB_(i) in the non-imageheating region AP is less than that of the image heating region AI torealize power saving of the image forming apparatus 100. In the presentembodiment, T_(AP) is set as 158° C. The reference temperature T_(AI) ofthe image heating region AI and the reference temperature T_(AP) of thenon-image heating region AP are preferably variable according to thetype of the recording material P, such as a thick paper or a thin paper.Moreover, the reference temperature may be adjusted according to imageinformation such as an image density or a pixel density.

Moreover, the temperature correction term K_(AI) of the image heatingregion AI and the temperature correction term K_(AP) of the non-imageheating region AP are set according to the heat accumulation count valueCT_(i) in each heating region A_(i), as illustrated in FIG. 8A,similarly to Embodiment 1.

Next, comparison of heat accumulation count values in the heating regionA_(i) (S1077) will be described. In S1077, it is determined whether theheat accumulation count value CT_(i) in each heating region A_(i)satisfies a heat accumulation count value comparison expressionillustrated in Table 1 below. In the present embodiment, the heataccumulation count values CT indicating the thermal history betweenheating regions A₁ and A₇, between heating regions A₂ and A₆, andbetween heating regions A₃ and A₅ that are at symmetric positions inrelation to the central position of the image heating apparatus 200 arecompared. That is, the heat accumulation count values CT in the heatingregions A_(i) formed by the pair of heat generating elements disposedsymmetrically in the longitudinal direction about the heat generatingelement disposed at the center in the longitudinal direction among theplurality of heat generating elements are compared with each other.Expression 1-7 is a heat accumulation count value comparison expressionfor comparing heating regions A₁ and A₇, and Expression 2-6 is a heataccumulation count value comparison expression for comparing heatingregions A₂ and A₆. Table 1 includes six heat accumulation count valuecomparison expressions for comparing heating regions.

In the present embodiment, S1, S2, and S3 are determination values fordetermining skew of the fixing film 202, and are set to 200.

TABLE 1 Control temperature correction Heat accumulation count Imageheating Non-image value comparison expression region heating region CT₁< CT₇-S₁ Expression 1-7 TGT₁ = T_(AI) − K_(AI) + TGT₁ = T_(AP) − S_(AI)K_(AP) + S_(AP) CT₂ < CT₆-S₂ Expression 2-6 TGT₂ = T_(AI) − K_(AI) +TGT₂ = T_(AP) − S_(AI) K_(AP) + S_(AP) CT₃ < CT₅-S₃ Expression 3-5 TGT₃= T_(AI) − K_(AI) + TGT₃ = T_(AP) − S_(AI) K_(AP) + S_(AP) CT₅ < CT₃-S₃Expression 5-3 TGT₅ = T_(AI) − K_(AI) + TGT₅ = T_(AP) − S_(AI) K_(AP) +S_(AP) CT₆ < CT₂-S₂ Expression 6-2 TGT₆ = T_(AI) − K_(AI) + TGT₆ =T_(AP) − S_(AI) K_(AP) + S_(AP) CT₇ < CT₁-S₁ Expression 7-1 TGT₇ =T_(AI) − K_(AI) + TGT₇ = T_(AP) − S_(AI) K_(AP) + S_(AP)

Comparison of heat accumulation count values will be described in detailusing Expression 1-7 as a representative example:CT ₁ <CT ₇ −S ₁  (Expression 1-7).

CT₁ is the heat accumulation count value in the heating region A₁, CT₇is the heat accumulation count value in the heating region A₇, and S₁ isa skew determination value of the fixing film 202 in the heating regionA₁. The skew determination value S₁ of the fixing film 202 is set to200.

In S1077, it is determined whether the fixing film 202 receives apredetermined level of a pulling force or greater in the longitudinaldirection of the image heating apparatus 200. As described above, theheat accumulation count value CT is a parameter correlated with the heataccumulation amount of the fixing apparatus 200 in each heating regionA_(i), and the greater the heat accumulation count value, the greaterthe heat accumulation amount. Therefore, the greater the heataccumulation count value CT, the greater the heat accumulation amount ofthe pressure roller 208, and the greater the outer diameter of thepressure roller. As described above, the heat accumulation count valueCT is a parameter correlated with the outer diameter of the pressureroller. Therefore, when the heat accumulation count value CT₁ becomesless than the heat accumulation count value CT₇, the outer diameter ofthe pressure roller in the heating region A₇ becomes greater than theouter diameter of the pressure roller in the heating region A₁, and apulling force of pulling the fixing film 202 from the heating region A₁toward the heating region A₇ is generated. Therefore, when the force ofpulling the fixing film 202 from the heating region A₁ toward theheating region A₇ increases, a pressing force applied to a flange memberthat holds a fixing film end (not illustrated) increases, and wearing ofthe fixing film end is accelerated. The same is true to comparison ofheat accumulation count values in the other heating regions.

When the heat accumulation count value comparison expression issatisfied in S1077, the control temperature is corrected (S1078). As forcontrol temperature correction, as illustrated in Table 1, the controltemperature TGT_(i) in the image heating region AI is set asTGT_(i)=T_(AI)−K_(AI)+S_(AI). The control temperature TGT_(i) in thenon-image heating region AP is set as TGT_(i)=T_(AP)−K_(AP)+S_(AP).T_(AI) is the reference temperature of the image heating region AI,K_(AI) is the temperature correction term of the image heating regionAI, S_(AT) is the skew correction term of the image heating region AI,and S_(AP) is the skew correction term of the non-image heating regionAP. In the present embodiment, the skew correction term S_(AI) of theimage heating region AI is set to 1° C., and the skew correction termS_(AP) of the non-image heating region AP is set to 35° C. By theabove-described setting, even when the image pattern illustrated inFIGS. 19A and 19B is printed continuously, it is possible to suppress anincrease in the difference in the heat accumulation count value betweenheating regions A_(i). Therefore, it is possible to suppress applicationof a pulling force in the longitudinal direction of the fixing film 202and to prevent acceleration of wearing of the fixing film end.

As described above, in the present embodiment, the control temperatureTGT_(i) of the respective heating regions A_(i) is determined accordingto the classification and the heat accumulation count value CT_(i) ofthe heating region A_(i). The setting values of the referencetemperature (T_(AI) and T_(AP)) of each heating region A_(i), thetemperature correction term (K_(AI) and K_(AP)) of each heating regionA_(i), and the skew correction term (S_(AI) and S_(AP)) of each heatingregion A_(i) are determined appropriately by taking the configuration ofthe image forming apparatus 100 and the fixing apparatus 200 and theprinting conditions into consideration. That is, these values are notlimited to the above-described values.

Next, the advantages of Embodiment 4 will be described by way of aheater control method using a comparative example and a specific exampleof Embodiment 4 to be described later will be described as a specificprinting example. In Embodiment 4, in a state in which the fixingapparatus 200 is in a room-temperature state (that is, a state in whichthe heat accumulation count value CT_(i) of each heating region A_(i) is0), 100 pages of a recording material (LTR size: a sheet width of 216mm, a sheet length of 279 mm, and a paper weight of 75 g/m²) illustratedin FIGS. 19A and 19B were printed continuously. It is assumed that theprinted image is disposed in the entire range in which the image passesthrough the heating regions A₅, A₆, and A₇ on the recording material P.FIG. 20A illustrates a change in the heat accumulation count valueCT_(i) of the heating region A_(i) with respect to the number of passingrecording materials in Embodiment 4.

Moreover, FIG. 20B illustrates a control temperature and a heataccumulation count value corresponding to the number of passing sheets.

In the comparative example, the control temperatures TGT_(i) of theimage heating region AI and the non-image heating region AP are setsimilarly to those of Embodiment 4 using the control flow of FIG. 11.

In FIG. 20A, a solid line indicates a change in the heat accumulationcount values CT₅ to CT₇ of the heating regions (A₅ to A₇) classified asthe image heating region AI in Embodiment 4. A two-dot chain lineindicates a change in the heat accumulation count values CT₁ to CT₄ ofthe heating regions (A₁ to A₄) classified as the non-image heatingregion AP. Moreover, for comparison, a broken line indicates a change inthe heat accumulation count values CT₁ to CT₄ of the heating regions (A₁to A₄) in Comparative Example 1. Since the heat accumulation countvalues CT₅ to CT₇ in Comparative Example 1 show the same change asEmbodiment 4, the description thereof will be omitted.

In the heating regions (A₅ to A₇) classified as the image heating regionAI in Embodiment 4, the heat accumulation count values CT₅ to CT₇increase as the number of printed pages increases. Since the heatingregions (As to A₇) are classified as the image heating region AI, thetemperature T_(AI) of the image heating region is set to 198° C., andthe heat accumulation count values CT₅ to CT₇ of the 55th page reach242. Moreover, since the heating regions (A_(i) to A₄) classified as thenon-image heating region AP are classified as the non-image heatingregion AP, the temperature T_(AP) of the image heating region is set to158° C. Therefore, although the heat accumulation count values CT₂ andCT₆ increase as the number of printed pages increases, since the heatgenerating quantity of the heat generating block HB_(i) is decreased,the heat accumulation count values CT₂ and CT₆ do not increase to begreater than the heat accumulation count values CT₅ to CT₇ of therecording material central region AM. The heat accumulation count valuesCT₂ and CT₆ of the 25th page reach 41. Therefore, Expressions 1-7, 2-6,and 3-5 that are heat accumulation count value comparison expressions inS1077 of the control flow illustrated in FIG. 18 are satisfied when thenumber of passing sheets reaches 55. Therefore, the control temperatureof the heating regions A₁, A₂, and A₃ is corrected according to Table 1for the 55th and subsequent pages (S1078). FromTGT₁=T_(AP)−K_(AP)+S_(AP), the control temperature TGT₁ is set to 193°C. Moreover, the control temperatures TGT₂ and TGT₃ are set to 193° C.in a similar manner.

As illustrated in FIG. 20A, an increase in the heat accumulation countvalue CT₁ for the 55th and subsequent pages is substantially equal tothat of the heat accumulation count value CT₇ corresponding to the imageheating region AI. Moreover, as illustrated in FIG. 20B, a heataccumulation amount difference CT₁−CT₇ in heating regions A₁ and A₇ ismaintained to approximately 200 and does not increase to a certain levelor greater. As described above, an outer diameter difference of thepressure roller between heating regions A_(i) at symmetric positions inrelation to the central position of the image heating apparatus 200 inthe direction orthogonal to the conveying direction of the recordingmaterial is set to 50 μm or smaller so that application of a pullingforce in the longitudinal direction of the fixing film 202 issuppressed. In this way, it is possible to prevent acceleration ofwearing of the fixing film end. Although the heat accumulation countvalue is a parameter correlated with the outer diameter of the pressureroller, the heat accumulation count value difference of 200 correspondsto a pressure roller outer diameter difference of 40 μm. Therefore, inthe specific printing example of Embodiment 4, the outer diameterdifference of the pressure roller between heating regions A_(i) atsymmetric positions can be maintained to be approximately 40 μm.Therefore, in Embodiment 4, it is possible to maintain the outerdiameter difference of the pressure roller between the heating regionsA₁ and A₇ to be within a certain range and to prevent acceleration ofwearing of a fixing film end by suppressing application of a pullingforce in the longitudinal direction of the fixing film 202. The sameadvantages are obtained for the other heating regions A_(i).

In the comparative example, as illustrated in FIGS. 20A and 20C, thedifference in the heat accumulation amount of the heating regions A₁ andA₇ increases as the number of passing sheets increases, such that theheat accumulation amount difference reaches 250 for the number ofpassing sheets of 80 and reaches 287 for the number of passing sheets of100. Therefore, in the comparative example, the outer diameterdifference between the central portion and the ends of the pressureroller is 50 μm or more when the number of passing sheets reaches 100,and the pulling force applied in the longitudinal direction of thefixing film 202 increases. Therefore, when the force of pulling thefixing film 202 from the heating region A₁ toward the heating region A₇increases, a pressing force applied to a flange member that holds afixing film end (not illustrated) increases, and wearing of the fixingfilm end is accelerated.

As described above, in the recording material edge PE, the difference inthe heat accumulation amount between the heating regions A_(i) in thelongitudinal direction of the image heating apparatus 200 does notincrease up to a certain level or more. Therefore, it is possible tomaintain the outer diameter difference of the pressure roller to bewithin a certain range and to suppress wearing of the fixing film endresulting from an increase in the pulling force. Moreover, by changingthe control temperature TGT_(i) between the image heating region AI andthe non-image heating region AP, it is possible to decrease the heatgenerating quantity of the non-image heating region AP and to achievepower saving.

The respective configurations of the above-described embodiments may becombined as much as possible.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

What is claimed is:
 1. An image heating apparatus for heating an imageformed on a recording material, comprising: a tubular film; a heaterprovided in an inner space of the film, the heater including anelongated substrate, a first heat generating element provided on thesubstrate, and a second heat generating element provided on thesubstrate at a position different from a position of the first heatgenerating element in a longitudinal direction of the heater orthogonalto a conveying direction of the recording material; a roller that comesinto contact with an outer surface of the film and forms a nip portionfor pinching and conveying the recording material between the film andthe roller; and a control portion configured to control electric powersupplied to the first and second heat generating elements, wherein theimage formed on the recording material is heated by the heat generatedby the heater at the nip portion, wherein the image heating apparatuscomprises an acquisition portion configured to acquire a first countvalue indicating a heat accumulation amount of a first heating regionheated by the first heat generating element and a second count valueindicating a heat accumulation amount of a second heating region heatedby the second heat generating element, and wherein the control portioncontrols electric power supplied to the first and second heat generatingelements so that a difference between the first count value and thesecond count value is maintained within a predetermined range.
 2. Theimage heating apparatus according to claim 1, wherein the first heatgenerating element is provided at a center of the heater in thelongitudinal direction of the heater, and the second heat generatingelement is provided farther from the center than the first heatgenerating element in the longitudinal direction of the heater.
 3. Theimage heating apparatus according to claim 1, wherein the first heatgenerating element is provided at a position where a conveyancereference of the recording material is provided in the longitudinaldirection of the heater, and the second heat generating element isprovided farther from the conveyance reference than the first heatgenerating element in the longitudinal direction of the heater.
 4. Theimage heating apparatus according to claim 1, wherein when thedifference is out of the predetermined range, the control portioncontrols the second heat generating element so that an amount of heatgenerating of the second heat generating element increases.
 5. The imageheating apparatus according to claim 1, wherein when the difference isout of the predetermined range, the control portion controls the firstand second heat generating elements so that a difference between anamount of heat generating of the first heat generating element and anamount of heat generating of the second heat generating elementincreases.
 6. The image heating apparatus according to claim 1, whereinthe first and second count values are updated for every predeterminedtime period.
 7. The image heating apparatus according to claim 6,wherein the first and second count values are acquired on the basis ofat least a heating history and a heat radiation history in a respectiveheating region.
 8. The image heating apparatus according to claim 7,wherein the heating history of the first count value is acquired on thebasis of at least one of a temperature of the first heating region andan amount of the electrical power supplied to the first heat generatingelement, and wherein the heating history of the second count value isacquired on the basis of at least one of a temperature of the secondheating region and an amount of the electrical power supplied to thesecond heat generating element.
 9. The image heating apparatus accordingto claim 7, wherein the heat radiation history of the first count valueis acquired on the basis of at least one of whether the recordingmaterial passes through the first heating region, a type of therecording material, a period in which the electrical power is notsupplied to the first heat generating element, and a change over time inthe temperature of the first heating region, and wherein the heatradiation history of the second count value is acquired on the basis ofat least one of whether the recording material passes through the secondheating region, a type of the recording material, a period in which theelectrical power is not supplied to the second heat generating element,and a change over time in the temperature of the second heating region.